I don't have anything against https://worldtimeapi.org/, which I use, but their FAQ makes it known that they are not to be relied upon for "commercial applications". Thus, it would be nice to have at least one "fallback API" to use if/when the first is shut down or goes down.
Please note that I do know about that NTP site, but I don't use NTP. I just want to fetch a JSON blob with the current time in it via HTTP(S), to check if the local time is not drifting too much away or is all wrong.
I don't know why NTP can't just be a JSON interface over HTTP(S) too, but it's not, so I sadly have little use of NTP servers from what I can tell.