Why do Americans spell words like "theatre" with "er" instead of "re" at the end?

@ChipmunkErnie Magic. Tragic. Pelagic; what??

@ffony If you say it like it ends in "er" then don't spell it "re".

@ChipmunkErnie OK Erny.

@ChipmunkErnie We do in my country. "Centre" and "theatre" are two examples.

@BijouPleasurette Yes, the British way. Just saw a video from a site that tells people how to speak "correct" English that claims there is no "r" pronounced in the word "core", that it should be said "cahw" -- the lady who teaches the lessons sounds like a poncy upper-class wanna be to me. ;)

?@ChipmunkErnie She's wrong. I'm doing it now: coRrrre - see?

@ffony We pronounce the "r" when it's followed by a word beginning with a vowel. "For example", for example. We sound the "r" on the end of "for". But when we say "For goodness' sakes" (or something more vulgar than that) we don't sound the "r".