Saying the Revolution was about taxes is a massive oversimplification.
Anyway, the whole "King Washington" nonsense is a bit of a pop culture tidbit that's wildly out of context and completely misunderstood.
There was no significant popular push towards establishing an American monarchy lead by Washington or anyone else.
The idea of making Washington king came in the context of an ongoing dispute between the Continental Army and Congress. Congress owed money to the troops but kept refusing to pay them, so some proposals were floated by certain officers and promptly shot down by Washington to organize a coup against Congress and make Washington king...as the officers expected Washington to be more sympathetic towards their cause and get them paid.
There's more to this story, but that the jist of it.