People who know better also say bedder instead of better. Language is really complex, Bayta is much smoother to say than Bet ta, it may or may not have something to do with it. I'm only speaking in really general terms though.
I say Bet ta myself, but I still much prefer the sound of Bayta.
I know full well it's said Bet- tah, but I say Bay-tah. I actually find it difficult to say it the proper way. I have studied many languages. Amongst them spanish, german, french, arabic, korean, japanese, as well as their corresponding writing systems. Also ancient mayan, hieratic, and egyptian hieroglyphics.
I WISH I could say that they all stuck... but I only speak fluent spanish and basic french now. I can still read korean and remember some hieroglyphs and very little arabic, but I do not speak any of the spoken languages.
I am also a former English Second Language teacher. I say all this because I can say, with a decent amount of experience for my age, that you can correct people all you want... but some people will just never say it the right way.
Look at it this way....
How do you say
Well... when I was in highschool, we had many students move to the farming area I lived in from Philly and NYC. They thought the way I said those words was just hilarious. The PROPER way to say "water" is Wah-ter. How do I say it? I'm from NEPA, I say wadder. Sorry... I do. I can't not say it like that.
I have tried time and time again to say it like Bet-tah.... but it just comes out very very forced. It may not be the proper way to say it, but you'll have to lump it in with the rest of the english language that changes pronunciation from area to area.
And yes... my name is Cassandra.... and I have always said it Cuh- SAN-druh
But many of my teachers in school, bosses in adulthood, and people I just meet say it "Cus-ON-druh"
Drove me nuts, but it was extremely common for people to say it both that way and what I saw as the "proper" way. Then I moved to latin america, and nobody there says the "A" in the way I say my name... so EVERYONE there called me "Cus-ON-druh".
Between that, and my extensive studies of languages, etymology, and having taught many people of various national origins the english language, I just learned that some words just do not have any 1 proper way. The Betta community may have a preferred pronunciation, but it is simply human nature to have varied pronunciations of the same word, and it does not make the person who says it one way any less ignorant or knowledgable on the topic than a person who says it a different way
If they know what the "proper" way to say it is, and they still say Bay-tah, let it be and accept it as them having been raised by different parents in a different area.