Some people collects stamps, baseball cards and spend a lot of time selling them, buying them. Are those people unlicensed money transmitter too?
No.
Is the higher frequency of exchange from fiat to bitcoin the main reason to be considered a money transmitter?
That is part of how the regulatory authorities decide where to draw the line, yes. Practically, though, money launderers have not gotten much use out of the collectibles trade. If they ever do, the regulatory framework could conceivably change to include it.
