For the overwhelming majority of people just becoming a permanent resident is more than enough - there's not a strong need to become a Japanese citizen vs. perm

For the overwhelming majority of people just becoming a permanent resident is more than enough - there's not a strong need to become a Japanese citizen vs. permanent residency outside of the right to vote, and for overwhelming majority, the trade-off isn't worth it. But Japan is not a particularly difficult country to naturalize in if you so desire. The N1 can be studied for and passed without being fluent. Supporting yourself financially basically means having roughly full-time employment. No idea where you got the idea you need to be married to a Japanese citizen, not true at all.