Its a company (and thus need to earn money somehow) and such usage data can be very useful for B2B marketing, which is what their core business is.
IMHO, opt out is a bit iffy, but if the admin of an instance doesn't even bother to go through all the settings to disable it, he/she will probably not care about the data send either.
Anyway, hosting your own Gitea is easy and simple. And for FOSS game related stuff you are welcome to move your code to our
https://git.freegamedev.net instance. It's hobby run though so there might be some rough times and I currently don't have a good backup system in place... I guess I should mention that on the page :/