Fiat also changes it value but not to much like bitcoin, so the first is the profit.
Then low transaction fees when sending bitcoin to the other part of the world.
Well yes, the supply of BTC will diminish so you get deflation instead of inflation. While this is very interested for holders, it also reduce liquidity as its push people to hold instead of spend.
Simply contrary to FIAT which lose value over time, so holding a debt in FIAT can be advantageous as it effectively shrink equivalent to inflation, which also mean that just holding FIAT in a bank account is bad unless you place it in a way that you at the very least get more interest on it than you lose to inflation.