One other reason is simply the cost of transferring from one register to another. For my own aircraft, which is pretty much exactly as it came from the factory with no mods of any significance, the estimated cost of transfer from the N to G registers was £7,000 if done at the same time as the annual. No physical changes would be needed, so that would be just inspection, paperwork and painting the new reg on the side.
Of course, once I come to sell it, it's also advantageous to still be on the N-reg. If I transferred to the G, there's a good chance it would cost another £7k to re-register it to the registry of wherever it's going, so a round-trip cost of £14k for nothing. On the N-reg it can either be sold back to the States or pretty much anywhere in Europe or the UK.