even if this game cost $10-30+ on itch, the dev is gonna sell the game again on Steam for the same price and we have to rebuy it again. It is not about the money/price it is about the principles.
Don't tell me that you are willing the rebuy the same AAA game on different platforms everytime (3x 50$ for example).
Without the itch support/funds, the Steam version will probably not exist.