Disagreed on several points.
First off, if you're using something like Sentry, chances are that building and running software is your job so it should not be a problem. If self-hosting Sentry is a problem I would start doubting the skills of your tech team.
Second, running a service for your own use is very different to running a service that has to scale to the entire world. Your service won't need as many moving & distributed parts as the SaaS Sentry since it will only ever have to handle a fraction of the latter's traffic.
Finally, if you're in control, you can schedule risky maintenance operations during times where a potential accident (operator error, etc) won't affect your business. You can't do that with an SaaS.