That is the problem with squadron owned stuff etc, lets say I create a squadron I invite all my friends, and we decide to have a fleet carrier, now since I am lazy, I do not have much credits, but the other have plenty of credits to ship and we fund the carrier. Now I think it would be super to have my own carrier, so I kick everyone from the squadron and now I am only user of Carrier...
This is what would happen in various ways, players taking advantage of other players, and even if noone have broken any rules etc, this is would be very bad behaviour and Frontier could get lots of negative PR from players doing this.
So I think this is was one the bigger reasons to make fleet carriers player owned and also all the players who do not play in a groupp that wanted the option to have a fleet carrier.
Then the issue with upkeep etc, having players the possibility to donate or whatever you want to call it, is a just a bad solution to a bad game mechanic...Why even have upkeep to begin with? what is the purpose for the upkeep? everything else in the game do not have an upkeep as that makes sense, imagine if there was upkeep on your ship? and if you took a break and ran out of credits and then you log back after a break from the game and to discover that most/all your ships are gone? This is bad user experience.
If upkeep only costed credits when you played, then it would not punish you for not playing the game. It would still be bad, but not as bad as it is now... as you can now take a break without having to worry about your stuff is gone when you get back. So once again, what purpose does upkeep server?
I think Fleet Carrier should have been like our ships, buy one for like 2 billion credits, and then you upgrade stuff, faster FSD cool downs, longer FSD range, better fuel effiency, add facilities like cartographer, etc and to max out your fleet carrier with everything would set you back some 8 billion more credits. So a relatively small entry step, but to a bigger task to max it out. and there would be no need to max out everything.