But even the default limits are high enough that there are plenty of companies that could at least in theory bankrupt themselves with it. Especially because there is no hard total cap, and so many services have high enough limits that you can get really nasty shocks if any one of them is maxed out. Even more so if you e.g. make use of different instance types (separate limits) in different regions (separate limits) and a wide range of services (separate limits).

And I've done work for clients that have requested really big increases because of both realistic and unrealistic expectations of handling traffic peaks. E.g. one client asked for an increase to 100 instances of 2-3 different types in a few regions to be prepared to handle a couple of days of high traffic. If said event had happened, they scaled it all up, and somehow didn't take them down again, it'd only take a few days of charges for them to be insolvent at their then-current funding level.

So you're right, there are limits, but limits or not doesn't matter if it's high enough that it can make you go out of business.

Which makes me wonder if anyone has ever gone out of business because AWS was unwilling to forgive a "surprise" bill. I'd be inclined to assume that they're willing to stretch quite far to avoid that, given that they seem to be very good about it. But I'd also not want to stake my business on hoping Amazon will be charitable about something like that.