I’m sure there’s an easy answer out there somewhere that I just don’t know how to google for, but anyway.
Honorific verbs like ござる and いらっしゃる (among others) don’t follow normal conjugation rules. By which I mostly mean they don’t turn that る to a り when adding ます, but instead turn it into a い. It’s ございます, not ござります.
Obviously I know to do that, and accept that it’s a thing, but I was wondering if anyone knew *why*. Is it an older now-outdated form of conjugation that stuck around? Why just honorific verbs (as far as I know)?
Edit: For the sake of completeness, the て/た forms are “regular” I think for most/all these verbs. いらっしゃって for instance, as opposed to いらっしゃいて or something like that.