This is done on purpose, to make people to switch to their e-mail or use them for hosting.

Google did the same thing with XMPP (they were welcomed when they joined, then they made it so XMPP users couldn’t message GTalk/Hangouts users, but the other way worked), they tried similar thing with Usenet, but they never get dominance there so they let their services to be major source of spam on Usenet until they were blocked, ultimately removing Usenet indexing from Google).

I would really encourage to contact our local reps (both federal as well as state) and encourage them to introduce legislation that would punish this practice.