What people usually want is all the bells and whistles of TCP without the occasional huge latency spike introduced by the guaranteed ordered packet delivery to the application layer.
Unfortunately, all the alternatives (SCTP etc etc) seem to have foundered, probably due to aggressive filtering by border routers/firewalls making it impossible for alternative protocols to gain traction.
Exactly my point about the whole "many variables involved", many networks still filter UDP as you say, which is really bad if you want to make sure everyone can use your game
SCTP droped 100% time as there no proper PNAT available for it. To make traction other protocols there need "happy eyeballs for transport" so it can be transparent for end-users
Unfortunately, all the alternatives (SCTP etc etc) seem to have foundered, probably due to aggressive filtering by border routers/firewalls making it impossible for alternative protocols to gain traction.