The only reason Ukraine continues to have Internet access is because the Russian Army hasn't chosen to cut it. That's literally it. Internet infrastructure is incredibly fragile. A couple of well-placed missiles is all it would take.
There's no excuse for Putin's invasion. None. There are underlying reasons but they are in absolutely no way a justification. We can and should ask how we could've avoided this. It may well inform how we end it.
That being said, Russia is clearly pursuing a strategy of minimizing civilian casualties (for now at least). Targets have been military installations, key geographic points, bridges, airports and command-and-control infrastructure. I suspect that if Russian casulaties continue (and it seems like they've been reasonably high) then images and video of downed Russian aircraft and helicopters and the remains of Russian convoys may well cause Russia to cut off that Internet. It could get much, much worse.