This is not about how easy or difficult it is to issue TLS certificates, to configure SSH keys or to update the OS. It's about having to actively maintain them yourself in every possible situation until eternity, like when TLS versions are deprecated, SSH key algorithms are quantum-hacked, backward-incompatible new OS LTS versions are released, and so on. You will always have new stuff come up that you need to take care of.

Exactly. Also, being that my specialty is writing software and not server maintenance, no matter how much of an effort I put forth there's substantial risk of blind spots where holes can lurk.

I felt more comfortable maintaining a VPS back between 2005 and 2015, but at that point attackers were dramatically less sophisticated and numerous and I was a lot more overconfident/naive. At least for solo operations I'm now inclined to use a PaaS… the exception to that is if said operation is my full time job (giving me ample time to make sure all bases are covered for keeping the VPS secure) or it's grown enough that I can justify hiring somebody to tend to it.