..why, because of the more contrasty look?
Not exclusively, it is because with a diffuser enlarger for a given light output from a 100w halogen bulb there is a light loss with diffusion. This means exposure times are a lot longer than they need to be even with a 75w bulb in a condenser enlarger. I was working yesterday in the darkroom and making 9.5x12 prints and the exposures varied between 35 and 45 seconds and that with with my Rodagon 50mm apo lens set at F5.6. That does not give me the best aperture to get the sharpest image which I have found to be F8 which of course would in theory double the exposure time. In addition the negatives I were using printed nicely without any filtration, I.E. G2. Introduce filtration and the exposures are getting longer again. When I print 120 negs, I use an older 80mm Rodagon with a maximum apperture of F5.6 and that has to be stopped down to F11 making exposure time quite a bit longer.
When I printed colour negs, the paper is so much more light sensitive, so even with quite dense filtration, exposure was only
very rarely in excess of 25s I no longer print colour - I was finding it too expensive so B&W won out.
I also used to own a simple Durst B&W enlarger (Now regrettably sold on) that would print up to 12x16 and with below lens filters the exposure times were around the 30-40s at most mark for a larger print, even with the lens stopped down to F8. But going back to your comment of a more contrasty image that also has it's downside because can accentuate grain and any dust or scratches, fortunately I did not seem have a real problem with any of them.
As an 'add on'. I could also use a LED bulb which consumes less power, produces more light, and does not heat up as much so I can use a glassless carrier with 120 negatives.
There are plusses and minuses between both diffusion and condenser systems, but on balance I think condensers are almost certainly better for my purposes