These are all poorly designed systems from a CX perspective (the billing systems).

Billing is usually event driven. Each spending instance (e.g. API call) generates an event.

Events go to queues/logs, aggregation is delayed.

You get alerts when aggregation happens, which if the aggregation service has a hiccup, can be many hours later (the service SLA and the billing aggregator SLA are different).

Even if you have hard limits, the limits trigger on the last known good aggregate, so a spike can make you overshoot the limit.

All of these protect the company, but not the customer.

If they really cared about customer experience, once a hard limit hits, that limit sets how much the customer pays until it is reset, period, regardless of any lags in billing event processing.

That pushes the incentive to build a good billing system. Any delays in aggregation potentially cost the provider money, so they will make it good (it's in their own best interest).

It's not typically a problem that usage is event driven. At least not for prepaid phone plans. Or debit cards. Or mailboxes. Or any myriad of prepaid or quota'd services. It's not rocket science, just a bad business practice on the part of Google.