What is the point of the RN to BSN programs?

I know that you need at least an Associate’s to become an RN (but it’s likely you won’t get hired with all the BSNs in the field?).
Why wouldn’t you go for a BSN right off the bat when becoming a nurse instead of waiting to become an RN w/ an Associate’s?
Is there a benefit to waiting to get a Bachelor’s?

Also, how long does an RN to BSN program take? I’ve looked on a bunch of different schools’ websites, and it doesn’t give you a time frame.