There's some confusion of order going on. In no state would it be illegal to buy someone else a ticket. However, if someone is being fined/arrested for riding without a fare, the crime(whether it should be considered that or not), has already been committed. Even if they could afford to buy a ticket themselves, making that purchase after the fact won't prevent the fine/arrest. So someone stepping in and offering to purchase a ticket doesn't change the outcome either.

Well as an example, my family and I were riding a Trax train (which is really a nice public transit system) and when we got off, there was a homeless person being pulled off by the police, and she was in tears and obviously very tired and didn't have a ticket.

I offered to buy it for her, I said, "whatever fare she owes, we can certainly pay it." But the officer said "No you can't do that under the law, she is required to buy it herself." But - how CAN she buy it herself in that situation? And why make the poor women feel even worse about herself.

It just made me angry, but Utah is a very restrictive place with a very authoritarian right-wing government, and there is no recourse for fighting back here. I don't blame the police, they know their jobs are on the line also.