Its because at a time you can select only one value from the parameters. You've assigned more than one value for single parameter so by default tableau will show the first value which you've put at the first position in selection. I'd suggest try to include Group Values (Car/Bikes ..etc) in your source then it will be easy for you to group them as per your requirement. That's the only workaround as per my knowledge.
I don't want to include group values in source as it will make other things complicated.
Then create a separate source for that and join with your primary source.