Because fleet carriers are expensive and should be able to make the owner money in my opinion.
Well that's not how the devs intended fleet carriers, the opposite is true. Fleet carriers were designed to be a black hole to throw money into, to try and fix the inflated economy somewhat. MMOs do this all the time after some years of players accruing billions of gold/credits whatever.
Of course, you can make money with an FC but it involves playing the game. As for them being expensive, I have all services enabled and my FC will run out of money in 11 years time, and I'm fairly poor as FC owners go.
If you want to make money using Vista Genomics, go do some exobiology because you'll make a lot. Then you'll understand why nobody will ever sell their data on your fleet carrier. Right now there is no incentive to do so. You don't lose your genomics data on dying, and it's not like the old days where you had to worry about interdictions on returning to the bubble, so you won't die anyway. If there's a tariff there will be an actual disincentive and people will just go to a station instead.
Bounties work a little differently because they can be scattered all over the bubble, so sometimes for convenience you'll take a 25% loss to avoid jumping all over to turn in bounties. Although nowdays a station's redemption office will even handle non local bounties for some reason, so Interstellar Factors and FC redemption offices are obsolete for that, but that's another story. If you get your way, FC Vista Genomics will become obsolete as well which is kind of amusing at this point.
Of course your idea would be fine if we can set a tariff to 0%, but why would it work differently from the redemption office which has a fixed tariff? We don't own the Vista Genomics even though we paid for it and even chose the employee, it's a private company setting up shop on our carrier. FD design has a lot of inconsistency to it, but sometimes it's there for a good reason like creating incentive or game balance etc. This is just another example imo. The bug is the service description rather than how the service works.