PTC is a lot more than overspeed control, imagine any use case that would be enabled by electronically controlled trains connected to a highly available network.
TPWS was always a stopgap (rolled out in the 90s while ETCS was being developed); as I said it was cheap and easy to deploy, and has prevented many accidents exactly like this one for 25 years
ETCS does what you are describing, and has been live in the UK and Europe since the early 00s
it works, and is slowly being rolled out everywhere replacing TPWS
so, again, why re-invent the wheel?
even the Chinese are adopting it