TPWS can enforce permanent speed restrictions, buffer stops, conditionally enforce speed towards signals at danger, and intervene if a train passes a signal at danger, but this intervention can only happen at the exact moment a train passes over a TPWS installation.
Intermittent communication, intermittent supervision, only two outcomes at each encounter with track installations – intervene, don't intervene.
BR's ATP offered intermittent communication but constant supervision, but that system was only installed on two main lines or so, and was later removed from the Chiltern. It's only now with the (somewhat slow) introduction of ETCS that constant supervision is being introduced more widely in GB.