There's plenty of specialized providers which provide this service, Verisign is one of many. The issue with on-demand BGP mitigation is that an attacker can do

There's plenty of specialized providers which provide this service, Verisign is one of many. The issue with on-demand BGP mitigation is that an attacker can do short attacks on and off over a long period of time. Each time the mitigation kicks in, BGP propagation takes at least ~1 minute and will cause some downtime. Proper protection is always-on without requiring redirection.