> MVNOs don't care

This is an excellent point

I assumed there would be anti-fraud measures blocking this kind of activity, but if this is a paying customer it isn't necessarily fraud/bad to the carrier or mvno

It'd depend on the mvno and their costs, but if the user fees pay for the underlying costs, the mvno is making money, and their user numbers go up, which makes for happy graphs.

They can also cancel or limit sims that do too much messaging or calling, which drives new user signups and makes more happy graphs. Doesn't really matter to them if all the abusers live in the same office.

Increased volume also likely reduces their unit costs with the underlying operator and messaging/calling providers, so even break even abusers help their bottom line by increasing margins for normal customers.