But city placement is supposed to matter, and if you could just ignore water for housing and luxuries for ammenities, a big part of that would be gone.
I'd argue that one of the hallmarks of civilization (humanity) is its ability to use engineering to compensate for the weak side of trade-offs. You only get 36 tiles - using 2-4 additional, and paying for them both with production and gold, would be an interesting decision for the player to make.