Crypto ads have been allowed on Google for a while already. Also, scams like this manage to get through because the ad submission part is mostly automated. It'd be incredibly unrealistic to expect Google employees to go through every single ad submission before they approve/decline them.
Go through every single ad submission no, but they don't seem to be doing anything with sites with domain names looking similar to domain names used by high-traffic sites. But
it's not that they aren't doing anything so perhaps they have other priorities and maybe cryptocurrency-related site scams aren't common enough for them to care.