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.
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?