lost my YouTube Icon and can't seem to get it back

If you're using a 2nd gen Apple TV then I'm afraid you're out of luck. Google has stopped support on older devices and thus it is no longer available.

This just happened to mine 30 minutes ago, it was replaced with TED icon. I used my YouTube all the time, why would Google stop supporting?

The technical explanation, is they changed something about their interface that would no longer be compatible with older software. As such, youtube on older devices that cannot be updated would stop working.

They could have just left older devices with the last compatible update, like most other apps do

Again, the changed something about their interface, that required an update to the Apps that the older devices did not get. The last update made to older devices would not work with it anymore. It needed a new update it could not get.

That is, the way the Apps connect to their service to get videos was changed. The old Apps that could not be updated would not be able to connect to it anymore because of the change.