Betty the Yeti was stuck in "B Mode".
A "B Mode" that would never be repaired for many reasons.
Betty knew this, and just stayed there in that one position, holding onto bits of broken train track, one arm outstretched. Which was where the nickname "Disco Yeti" came from.
Though that was more about the strobe light effect to give the illusion of movement.
It had been many years since Betty last moved. And would likely never, ever do so again.
Though Betty had long accepted that fate and was happy now as a 25 foot figure than an animatronic.
Betty the Yeti is a boy, but is called Betty by cast members, because Betty rhymes with Yeti (the ones over at the Matterhorn Bobsleds in Disneyland in California are called Harold though). So I kept the gender ambiguous. You can read Betty as being either a boy or girl.
And yes, it really is referred to as the Disco Yeti because it operates in "B Mode". A Mode would be it moving. But because of a fault in the foundation, it can't move. And 5th can't fix it because that'd mean taking apart the ride. Or so it's believed - nobody really knows the real story behind it except imagineers.
I suppose it could also be an allegory for disability. Why not? Yeah. The Disco Yeti is disabled. And I suppose it's canon. Not to the ride's storyline, but still.