Not all European practices are better
Recently, I was in north east Germany and experienced the transport systems of a number of cities. It is quite normal for drivers not to sell tickets, allowing them to concentrate on the safe carriage of their passengers. Those not already holding tickets and boarding where there is not a pavement ticket machine are directed to the onboard vending machine.
Remember when First tried this out on the Streetcars in York leading to queues, the same problem still exists in Schwerin, the state capital of Mecklenberg-Vorpommern. Like most cities in the area, Schwerin runs three door rigid Citaros but practices boarding through the front door only. No problem if most people have tickets but half a dozen unfamiliar visitors boarding outside a hotel is another matter. The ticket machine is over the offside wheelarch meaning anybody using it all but blocks the gangway, two stops further on and boarding passengers were still having to squeeze past those using the machine.
A hundred miles further east, Rostock has mainly articulated Citaros to a similar multi door specification but the ticket machine is opposite the second door where there is plenty of circulation space and passengers normally have no need to queue onto the front platform.