"Because this type of compression sounds better to me today in this room on this track in this piece of music" is always going to be my answer. Rules and theories are only helpful until the time they distract you from listening to what's actually stroking your eardrums, I think.
And all the information is out there, for anyone who actually wants to dive into it the technicalities of the characteristics of different circuits. And on an intellectual level it's fairly interesting stuff - how valves are biased, why FETs sound like they do etc. I like reading about that stuff, personally.
But everyone, from the greenest of the green to the proest of the pro, will make their choice of compressor based on experience of what's worked or not worked for them in the past. And if they don't know what'll work best, they'll try a few things and see what sticks. The in-depth technical knowledge will just allow them to intellectually explain why it worked, it won't help them mix better.
I'd probably also go so far as to say that if someone doesn't have the experience and picks their compression type with confidence based on things they've read rather than things they've felt, it might even slow down their progress to understanding compression as a practical tool, just because in the confidence of knowing their actions conform to general good practice, they might not try some wild ideas.
Usual disclaimers - all my opinion, more than one way to skin a cat, lots of different roads to the same place, everyone's different etc. This is just a reflection of my own attitude to mixing where I don't want to be thinking too much.