First reasons why i don't want that this one relay of mine is a fallback:

1. It is heavily used and can barely keep up with the traffic.

Even if fallback traffic is low i have plenty of other relays that are bored right now.

2. I plan to switch it to an exit maybe and i don't think exits should be fallbacks.

They draw attention, they are blacklisted, they are hated and depending in which country they are maybe even watched by some higher authority.

So i think users connecting to fallbacks that are exits should be avoided.

Again i have plenty of other relays that are no exits and where i don't plan to make them exits so i think these ones are better for being a fallback.

Not related to that one relay but other reasons why i don't want that some relays of mine are fallbacks:

3. I have relays in countries where the government doesn't really like Tor.

If my provider would be forced to shut them down (or just shut them down because he doesn't like Tor) then if the relay is not a fallback soon after it went down no users will try to connect to it anymore and after a week or two it is gone from metrics.

If it is a fallback then for weeks, months maybe even years users with old Tor versions will try to connect to these addresses because Tor expects a fallback there.

Maybe having fallbacks in these countries is even more important but again as long as i have relays that are really bored and as long as i can only opt-in a limited amount of relays i prefer to choose ones that are not located in these countries and maybe it even helps my provider with not getting any future problems with their regime.

4. I didn't checked it but some provider have a crazy TOS and i would not be surprised if some of them write there that it is not allowed to hardcode the IP you get from them into anything to prevent them from reason 3 where old versions of a software are abusing their IPs when it is already long gone.

But exactly that is what you do with opting-in as a fallback.

Maybe there are more reasons but these are the ones i have in my head right now.

It is not the end of the world that this one relay is a fallback now.

But it is surprising because that particular fingerprint never got opted-in by me so i think something went wrong somewhere.