It's a tradeoff between concentrating your risks in a very low-risk-probability monoculture or distributing your risks across a large statistical sample of (generally) much higher risk individual providers (smaller companies shut down or get acquired at much higher rates, and are frequently still high value targets for attackers even though they have much smaller budgets to spend on security and defense).

Distributing your risk among a large number of vendors is not necessarily better, and even if it's "just backups" can still multiply your risk of ideally non-public information getting disclosed.

Denial of service risks exist but are rare and, for example with the myriad complaints about "stripe is evil" tend to trace back to "account in question was doing something a rational unaffiliated observer would predict as a likely account cancellation driver for stripe." We don't know the circumstances here. If the circumstances were benign, it will likely be corrected, if not benign, we may never know the details.

EDIT ADDED (since HN is rate limiting this): self-hosting doesn't eliminate risks, it just changes them. You still face denial of service risks from loss of power, fire, natural disaster, theft, component failures, etc. If there were a zero risk path, everyone would take it.

We tend to prefer risks we feel we have "control over" (eg. Self-hosting), but at the incident rates of most other corporate hosting risks you're into the territory of an earthquake took out both your house and your rented storage locker.