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Im just assuming that they could shift to other coins for the sake of mining.
They could, assuming the other coin also use SHA-256. But usually it'll be less profitable and if too many Bitcoin miners move to that coin, the difficulty would be increased to the point it become no longer profitable. Similar phenomena already happened with Ethereum miner[1].
Well, other people do use much higher sats/byte in their transaction even though they amount they transact is not much.
It's partially because some service/wallet set fee high enough so transaction will be included on next block. Or worse, use website which considered malicious such as bitcoinfees by earn.com[2]
[1]
https://www.tomshardware.com/news/gpu-mining-is-now-unprofitable[2]
https://bitcoinfees.earn.com/