You'd have to break most of those platforms' TOS to do so.

That's always been the case. Jailbreaking your phone is also breaking TOS. Sideloading apps on iPhone by using the developer features is breaking TOS. Almost anything that gives a corporation less money or control over you is against that corporation's TOS. That's not the law, though, and we need to grow a collective spine.

... It's a lot easier to have a spine about risking getting banned from a service if getting banned from that service wouldn't destroy your life.

Was Pidgin TOS-compliant back in the day? I'm a young whippersnapper, so I don't have experience with it myself.

Well it did have to change its name from GAIM to Pidgin at some point because it infringed on "AIM" by AOL. And whether or not Pidgin was fully "TOS-compliant" (which it might have been depending on the service we'd be looking at) is not as relevant as whether these terms would have been actually legally enforceable or not.

That was due to a trademark violation and nothing to do with TOS.

We (Pidgin/Gaim/Finch/libpurple) have never been TOS compliant.