Why would I want a Roth IRA vs traditional. Won’t I theoretically be making $0 not counting withdrawals when I retire?

If I was retired and living off my investments and social security what are the odds that I'm making more than when I was working? Maybe I'm missing something but whenever I see this recommendation and people say "if you expect to be in a higher tax bracket than you are now". Wouldn't my income basically just be the withdrawals?