Earlier quoted context omitted.
All these services have free plans either if you have little traffic or if it's open source. So it's definitely possible to self host this (although maybe not completely trivial). Disclaimer: I work at Stream (but haven't really worked on Winds)
An outage at any one of five services will stop your thing from working, and it won't necessarily be obvious what happened. Now you need to monitor five services, plus the one you actually built. Oh, and the free plans will stop being free once you cross a threshold of use, which is probably about when it becomes important to you. If each of those services has an outage once a year, you'll get to feel all of them. Co…
Meanwhile, obtaining anything over 99.9% is usually a challenge for the amateur. Even if you are on call on every day of the year, it's very easy to go to sleep with your phone muted and wake up the next morning to discover the service is down for whatever reason.