Inputs spending outputs with the same locking script repeat some of the input elements necessary to spend the input. E.g. a P2PKH input needs to reveal the public key corresponding to the public key hash appearing in the corresponding transaction output’s output script. This would need to happen again if someone spends another output with the same output script.

If we made reusing the same address cheaper that would undermine the privacy best-practice of using a new output script for every payment. I therefore see zero chance of such a change being adopted in Bitcoin.