GPL aims is "If someone uses code you open source, then all users can get the source of that app"

In the past, external users would mostly get software they ran themselves. Hence GPL2 "share-alike" kicks in when software is *distributed*

Today, many many people access software of the internet (SaaS etc). GPL2/3 doesn't guarantee users access to source code, so it's against the spirit & aim

I get the BSD v GPL difference. I see why people say "BSD is more free", and that's fine. It's your code, licence it how you like

But I'm not sure why someone would choose GPL2/3 over AGPL!

The point of GPL is ensure users have the source! So why not ensure that? Why not use AGPL??

AGPL (or GPL to a degree) is not much liked by corporations. Some see this as a disadvantage. I see it as an advantage.