I look at things this way : many of those mechanical cameras were built to last. Later electronic ones were often marketed on the presumption people would want the latest and greatest bells n whistles every few years instead. So it depends on what condition that mechanical camera might be in when you buy it. The only 35mm camera I still use is a mechanical FM2n, which I bought new; and I'm quite certain it will long outlast me. Other mechanical 35's I've owned included the venerable early Pentax H1a and the Pentax MX. Both went through utter hell in the mountains and deserts. A shutter speed gear finally wore out on the H1a, and the MX went to my nephew who used it for multiple extreme climbing expeditions in the Arctic, Andes, Karakoram, and Himalyas, among numerous other places, and it did fine the whole time.
I don't think that could be said about fancier or electronic cameras; it heard nothing but complaints from mountaineers who tried those. One of them, a Himalayan super-star climber, went back to his FM2n.
But for forty years, I shot almost nothing in the mountains except view cameras, which are obviously mechanical in every respect. Once in awhile, getting older, mechanical MF gear, like my Fuji 6x9 RF's.