CloudFlare has a "Auto" TTL option, which is the default, and required to be used when reverse proxying through CloudFlare. There is nothing magical about "Auto" TTL, though: it appears to literally always be 299 seconds. A lot of low TTLs you see are probably caused by CloudFlare.
Similarly, AWS Route 53 alias records use a 60 second TTL and there's no way to change that, so that's probably about a quarter of the Internet right there. Also when creating a manual record in Route 53, the default is 300 seconds and you'd have to go out of your way to pick another value.
