It's not a strategy. It's technically difficult, opens them to liability if runaway happens so fast their system can't stop it, and is only wanted by bottom of the barrel customers.

Just a thought: Maybe if they had some kind of opt-in insurance against overuse until the circuit breaker can kick in?

But, looking from the outside, the lack of protection is effectively a win for them. They don't need to invest in building that out, and their revenue is increased by not having it (if you ignore the effect of throttling adoption). So I have always assumed that there is simply no business case for that, so why bother?