These providers operate across multiple platforms and share intelligence about suspicious behavior, including arbitrage patterns. If you’re taking one side of a market on one site and the opposite on another — they see both sides. 
It’s normal for them to become aggressive because all this bookie will suffer shared losses if they allow continuous arbitrage betting due to +EV on every bets.
This is a huge amount of loss from all of them if there’s a bunch of user doing this method on large scale bet. As business, they will not allow a guaranteed profit because their operations profit will be affected.