I understand the cynicism, but I think it's unfounded.
"Jail" is a term often used in computing to describe a sandboxed environment. E.g., "a chroot jail" in Unix, used to run a process in a contained filesystem so any exploit against that process doesn't have access to the full system. Since modern mobile devices run pretty much everything in a sandbox, "jailbreaking" them merely pertains to running processes outside of that constraint. It does not necessarily imply the constraint is imposed upon you against your will. Many browsers run processes this way, for e.g., and I am all for that.
I would love to debate the finer points of walled-garden ecosystems, because I think it's a paradigm that offers a lot of advantages, and some obvious disadvantages. A part of my career involves secure computing and I absolutely understand the dilemma, and root equally for both sides of it. It's a hard line to draw and remain equitable to everyone involved. But that is likely to derail this thread, and I've done that probably more times than is fair already.