Why are US banks closed during hours when it’s most convenient for many customers (evenings/weekends), and how does that make business sense?

Many banks have done studies on this, not just US Banks. Whilst there is certainly a demand in the evenings and weekends, considering all the other banking partners that banks have to work with (who are not open after hours and on weekends), banks lose out a very small market segments that sees an immediate need for banking after hours/weekend.

If banks were to open on weekend/off-hours, statistically (from a business point of view), they earn very little income. Traffic numbers are very low. So all-in-all, closing on weekends/after-hours is not bad for them.