Technical, weight, and reliability issues, I reckon. Also noise. Most definitely not the camera for wildlife photography, tho I've read of an Indian pro who did just that for many years. The sound of an EL shooting an image would spook a herd of elephants. I've owned three from the mid '90s, two ELs and an ELM, and finally sold them on Ebay last year, as a job lot, for a fraction of what they had cost me, to a collector who loves tinkering with them and bringing them back to useful functionality. I wish him luck. And hope he is spared the inevitable nervous breakdown...
When they worked, they worked well, sort of. #1 EL malfunctioned during an architectural shoot in a church in Melbourne. It just jammed up and refused to fire off the lens or wind film. Fortunately I had a Rolleiflex TLR in my kit, also a Rollei panorama head, and I completed the shoot with it. The parish priest knew cameras and watched me with raised eyebrows, but after much much post processing work, he and the client loved the results. My hair went two shades whiter during that shoot, but I did it. Many thanks to Rollei Werke! The repair to that EL cost me almost the price of the camera. Boo hoo!
#2 EL (a bargain buy from Ebay) blew the side battery panel off when I first plugged the (original) charger to the camera. No-one died and nothing fell over, but the explosion scared several lives out of our cats, and SWMBO then banned me forevermore from using or charging an EL in the house. I eventually repaired this one at home, and got the el cheapo 6V battery holder for it. It then functioned sort of okay for five years, but occasionally refused to do anything even with a new battery, and of course went thru batteries like a drunk goes thru beer.
#3 (an ELM) looked as new and worked mostly okay, when someone else was using it. It hated me and had it in for me. I still did weddings then, and I enjoyed the good impression my bridal parties had when I put the hateful thing on a tripod with bounced lights everywhere and fired off the motor. After a few good shoots it took to running the entire roll of 120 film, from start to end, ripping off bits of backing paper as it whirred thru the rolls, making them unusable again even in my Rollei TLR. After two disastrous weddings (also finished with the aforementioned Rollei, which if anything impressed the wedding participants even more), it became a shelf queen in my home office.
In 2010 I happened to be passing a leading and very reliable Melbourne retail camera shop, and having stopped to look in their used gear window, spotted a beaut 500CM (1986 model) with a late '90s 80 f/2.8 T Planar, two A12 backs and an almost mint chimney finder, on sale for A$850. Wrongly priced, I thought (correct, as I later learned.) In an interesting coincidence I had given this shop a camera on consignment a few years before, and then forgot about it, and when I went in to finalise the purchase, I was surprised (and certainly delighted) to discover I had a several years old credit of A$350 on file, which greatly sweetened the deal.
I gave up weddings long ago to preserve what remained of my sanity and I now no longer do commercial photo work, so since I've owned it I have used the 500CM for at most 30 rolls of film, largely to reduce my now-ancient stocks of frozen Ektachrome 100 and Fuji Velvia films. It's a lovely machine to work with and my results have been no less than exquisite, tho nothing the Rollei TLR wouldn't do with much less effort and certainly far less weight. (A valuable lesson here, folks...)
As happens to every 'blad user, when one owns an EL or a 500CM the accessories just seem to collect like breeding rabbits. I now have two cartons of them, all purchased at good prices some years back when prices on all those goodies (and indeed the cameras) were down in the doldrums. Suddenly people want Hasselblads again, and kits appear to be selling better than only cameras or accessories being flogged separately.
All the above to say that later this year when I am home again (I'm overseas now), I will be biting the proverbial bullet and putting the 500CM on sale, then the lenses (50, 150 and 250), and finally the accessories,with the cheerful thought that at today's OL prices, I will (I hope) make small profits on the lot. And someone will get a truly fine camera to use for the next umpteen years, probably long after I'm gone.
To me, and with all due respect to those who still use and love them, the ELs and ELMs are now period pieces and bordering on the ancient. They seem to work well while they work, but woe unto you if and when you have to get them repaired (and you will, trust me on this). The shops see you coming, and nowadays Hasselblad repairs and spare parts seem to increase in price in increments of US$100 at a time, with no change being returned. The 500Cs (I know a few people who use them, and love them dearly) and the newer 500CMs can also be expensive to repair, but being totally mechanical, seem to need much less maintenance. My 500CM was last serviced in 2005 (I have the original docs) and may well never have to be redone. They are not young cameras, and with careful and sensible use, will likely go on shooting for a very long time.
My comparison, my Rollei (an E2 with a 3.5 Planar, for the record) was bought as a two year old and has had only two servicings in its 54 year life. Its only drawback, for me, is that I cannot change the lenses. As for the rest, it does everything it does with precision and quiet reliability.
Most posters here sing the same refrain, buy the ELs or ELMs because they are so cheap. This to me smacks of false economy. Better to save up and get a 500C, CM or 501CM. IF you get a good one, any of the latter two will outlast you.