I was curious all of a sudden - never thought about it until now, so thanks @wildone and Val - so I asked Mr Google.
This answers both your questions:
https://www.quora.com/Why-do-we-say-a-pair-of-pants-when-referring-to-a-single-pair
I loved everyone’s answers as well, but what really struck me was what @AC Benus named as his early childhood influences. I’ve never thought of nursery rhymes or Dr. Seuss as being poetry, but yes, they really are. So cool, to realize that.
PS: I had a Puss N’ Boots storybook, too.