I believe that's because devs want to use what they use for their workstation (that is, what they know the best) on their servers. That's understandable, and most cloud services give you boxes that are already usable but because you don't have sth. like the FreeBSD handbook, and because the whole thing is not that thightly integrated, complex stuff requires hacks and dirty workarounds or at least a lot of experience. I have not done any system-admin work, but I can say this: in one week I've managed to make my FreeBSD system completely reproducible after using it for the first time. I haven't been able to do that with any Gnu/Linux, and I've used it for more than ten years till last february I guess.