This is a phrase that we use. So they just are what they are. See also "black and white" not "white and black". I'd also avoid "we're" in fact that is the first time I have ever seen it written. "We are" is clear.

Oh I found this to explain why it is Black and White, not White and Black https://www.theguardian.com/commentisfree/2016/sep/13/sentence-order-adjectives-rule-elements-of-eloquence-dictionary

Thanks, Paul. I was just trying to make my writing seem less dull.

Don't worry about the 'why', just accept the way it is. That's how collocations work. 'Forth and back' sounds very strange. 'Back and forth' sounds fine. Btw, what's with the 'ain't?' I know your English is of a decent enough level to know that this is a controversial word in English, people don't write it unless they're trying to imitate speech. Serious question, have you ever seen a native speaker, from any country, use it on this website? I would wager no. We just don't use it when we're writing normally, it sticks out a lot.