Checking tickets can be done by not allowing anyone on the platform. Or world best practice is random checks and large fines if you are caught without a ticket.
Breaking rules is tricky. There is some need for that, though there are options, though in the end I will grant you this.
Trains should never serve food or drink. Passengers can get off the train at a station when they need that, and get on the next train. Space used for the food and drink is space that could be used for more seats. There is a reason all railroads have been trying to do away with food and drink service. It is considered bad practice everywhere.
> Trains should never serve food or drink. Passengers can get off the train at a station.
There aren't going to be stations all across Nebraska or what have you. And even if there were, stopping repeatedly would defeat the purpose of high-speed rail. All that time speeding up and slowing down starts to add up very quickly.
Don't forget it would massively extend every stop. At least an hour+ at each station if you expect every passenger to detrain (with their luggage, because they're not leaving it on the train), wait in line, probably dawdle and then reboard.
* Check passenger tickets
* Observe the cars & make sure people aren't breaking rules, etc
* Serve food/drink if applicable (e.g. for business class)
And so forth. This is how the KTX and Shinkansen work, and they know what they're doing.