First, can I correct your questions? To ask questions, you need the word 'Why?' (not because) 'Why are 'Get in the car' and 'Get on the bus' different?' 'Why is 'Get on the car' wrong? The answer : We use 'on' for public transport, like 'bus', 'train', 'tram'. 'boat' We use 'in' for cars and taxis.

In English we get "in" small vehicles and we get "on" large ones. We get in a car, but we get on boats, trains, planes, boats etc.

Good question...something that probably never occurs to native English speakers. Yes, we say "Get in the car." ("Get INSIDE the car") "Get on the car" would mean you want someone to physically sit on TOP of the car, on the hood or roof or something (so not an everyday behavior).

Good question. I have the same doubt.

"why", not "because"