In Chicago the whole system was designed for you to pay before you get on. There’s a turnstile to get into the station, and you can only get on the front of the bus and tap before you enter. So fares are actually a large percentage of the budget (I looked it up, it’s about 35% pre-pandemic, post pandemic the numbers got all weird). I have no idea why the system is designed in SF where you can essentially “jump” on for free and never pay.