This is purely and simply not true.I noticed that many FC owners are focused mostly on maintaining their carrier rather than enjoying things this game has to offer
I've had a carrier since they were released. There hasn't been a single day where I've had to worry about its upkeep costs.
I moved my entire fleet out to Colonia recently and just doing boring old BGS work (no mining or bulk trading) for the local factions is netting me >200M credits per week. The carrier upkeep is around 20M per week.
I set an arbitrary amount (40B in my case) for my CMDR account. Each Monday I transfer anything over that amount into my FC account. Currently my carrier can survive without any additional payments for almost 7 years.