Why do casual acquaintances wish to become FB friends?

In the past week I have been contacted by a renter from ten or eleven years back who moved to Florida and a former secretary from where I worked and I have not seen nor heard from in over 20 years since she moved to Phoenix.
I liked both ladies but we did not socialize nor have a relationship outside of renter/landlord or work associate type.
The only thing we have in common, to my knowledge, is that many years ago we knew each other for a period of time.
I don’t want to be rude, but I really have no interest and so will not.
But, what is the draw? Why reach out to those who you would do nothing but have an awkward, somewhat uncomfortable moment with were you to both meet on the streets. I have viewed their pages while writing this and both have between 150 and 250 “friends” so it is not like they need another sounding board. I don’t understand it.