Based on looking at V8's JITed code, there seemed to be a lot of overhead with stack overflow checking, actually. The function prologues and epilogues were just as bloated in the tail-call case. I'll upload some screenshots if I can find them.
Good point, full self driving probably felt like marketing win back then... but now it is a liability.
Rebranding now would just highlight all missed promises
Found good visual explainer on this - https://vectree.io/c/linux-virtual-memory-swap-oom-killer-vs...