Because I know you missed it. Okay, I missed it. And in that vein…
Miss, as in to not hit or escape notice, comes from the Old Englishmissan (with the same meaning) and the Proto Germanicmissjan, meaning “to go wrong”. Now missjan comes from another Proto Germanic word, missa-, which means “in a changed manner”. From changed manner we get abnormal, incorrect, from there we get to go wrong, and from there we get our current definition. So miss changed with each incarnation, but the “wrong” sense of the word has always been there, and is the root for all the other definitions (to avoid, to not be on time, to miss a person or thing).
The other miss is the title for unmarried women. It’s actually short for mistressand before it meant young woman it meant, of course, prostitute or concubine. Yeah. We also have missus as the title of married women. The word is what’s called a corruption, in this case of mistress. Basically, people started saying it wrongly and it stuck. Before 1833, it had all the same definitions as the plural of mistress—more than one female teacher, or woman in authority, etc. But then people started using it as the title of a wife, despite the word being a plural. In fact, when you see, say, two unmarried sisters and you refer to them by their last names, it’s “the misses”, same pronunciation as one married woman with the same last name. So two married woman would be…the missuses?
Ah, linguistics. You do love to be confusing. It does explain the m, r, and s in Mrs., I suppose.
TL;DR: The title miss is short for a word that has nothing to do with the “gone” miss.
Tony Jebson’s page on The Origins of Old English