I'm fairly certain I've said this at one point before, but it doesn't bother me. I know what the proper terminology is, and I've honestly tried to say Betta properly for a while now, but my mouth has a really hard time talking around that word. That sounds weird, but Bayta is much more natural to my mouth so it is the way I choose to say it.
It also can very much be a "where I'm from thing" I really wouldn't turn my nose up to people who say that. I have a cousin that I moved close to a few years ago. We grew close and we were playing cards one day, her, myself and my brother's kids and she said the word King as "Kin". After a bit of dialogue between us all, we found out she legitimately cannot pronounce the "ing" sound. We tried for about an hour trying to help her to it, but sometimes it just can't be done. It might seem easy to some people, but it can be really difficult, and a good amount of people who've taken a second+ language probably knows how difficult pronunciation can be sometimes. It does happen in English to English transitions.
I would much rather focus on the care of a betta, just like I'm not going to break it down into linguistics either. It's betta not Bedda, better, not bedder, butter, not budder etc. I respect everyone's opinion, but after a few experiences of my own, after the initial correction I refuse to let it bother me, because it might not be a preference thing all the time.