I agree, 'Theater is better than theatre but like us there is a lot more to do. 'Malapropism.' How ridiculous for silly use of words.
The fault lays squarely on the feet of whoever decided to send British colonists here to begin with. Whilst English remained English and even evolved somewhat in England, the colonists had to adapt and intermix the languages of the Spanish, French, Dutch, and whoever else decided to park themselves in this country. ( Not to mention the folks who are indigenous to this country. ) We do not speak and write English anyway, we write in ‘Merican with a little international thrown in just to make us look like we know how to communicate
Yet, every movie theater owner or theater group in the US who wants to appear artsy will revert to the British spelling of theatre.