Why did my iPhone Calendar wipe out all appointments?

This is the second time that I’ve lost ALL saved appointments/engagements in my phone calendar. Such an annoying thing when you save work things plus doctors appointments in it. I tried all suggestions to recover by going to iCloud and recovering that way but nothing worked. I noticed this time that my saved appointments in “purple” which is titled “WORK” were saved & restored, but, I choose the RED U.S. calendar as my default to see national holidays, & none of those appointments were recovered and I’m thinking it’s because those are NOT saved to the cloud, but Home or Work are saved to the cloud. I’m not sure if I’ll solve future issues like this from happening again if I enter all my new appointments and choose purple or blue (Home or Work) instead of the Red US calendar , but I’m trying that from now on. I NEED my appointments to be saved, not lost!!!!

Does anyone know if I’m correct on this?

[Re-Titled by Moderator]