About 10 years ago I got $100 for free to use on AdSense. I used it for fun not realizing it keeps going and then billed me. Since then I basically don't use any Google paid products. Hope that $250 was worth it.
That's... pretty much how every free trial works? Try signing up for a free month of Amazon Prime or Netflix and see what happens. The entire point of the promotion is retention.
It wasn't a subscription. My expectation was that it would simply stop once it hit $0. Not really here to argue about it. The tldr is I don't trust Google with this stuff anymore.