The major doesn’t necessarily cost more.
Factored into that number is personal and travel expenses. Not everyone has the same expenses.
My son is in engineering and his cost the past two years, (tuition, room/board, books, sports pass (parking only 1st year) was roughly 21K. That includes no club/organization costs, eating out, incidentals, or living allowance. He works full time in summers, so he takes care of his living allowance and budgets accordingly.
There are club/organization costs
Gas to come home and go back
Eating out (some on campus eateries have free food at closing)
So,while you have one set of expenses billed by university, there are other costs and it could creep up a few thousand more in what you decide/need to spend money on.