I won't parrot the reasons, I think other comments captured that.
However, I would MUCH rather share links in professional circles to something called programming.dev that is specifically an instance about programming rather than "choose your random generic instance" that has porn, memes, shit posts, etc. and oh look, a programming community too.
A lot of the time I don't even know where a post is coming from. They show up on my mastodon feed, I reply. I've clicked source links before and gone to completely new lemmy instances I never knew about.
I think, for some cases, it would make sense for an instance to host just a single community or a "family" of communities. programming.dev is a good example of this. Hopefully this will happen organically (communities will consolidate in instances that make the most sense for them).