This is a very good point. I pay more in state income taxes than the $10k cap, which means I don't get any real estate tax write offs. My now wife completely lost her $10k salt deduction after the marriage.

I have hatred for life.

The biggest item on SALT is the real estate taxes and mortgage interest expense. A household has only one address - and thus it makes sense to have tax deduction for just one real estate/ mortgage interest expense. As such it makes sense to share the SALT cap - just like sharing the home.

(also the fact that biggest beneficiaries of SALT are states either high housing costs and these states tend to be Democrat leaning states made it easy for Trump to cap the SALT deduction in his 2018 tax cuts)