Any idea why?

The "internal" memo: https://www.businessinsider.com/microsoft-is-offering-buyout...

So "Up to" 39 weeks of base pay, let's say 9 months.

In this job market, that may not be enough time to feel comfortable and safe taking the offer (if you're a super-employable hotshot with offers awaiting in your LinkedIn, you're probably not the likely target for the offer)

The prior VRP shook out a number of folks who were banking their options grants -- it was like "look let's be clear, you're not moving up any more and you're checked out. Thank you for your service." I'd imagine they were happy enough with that to go a little broader. The pay scales work out to getting paid more the longer you've been there. Mentioned in the memo is employee choice, and I think that this is likely designed with that in mind - why not let people self identify without penalty when you want to reduce headcount? The goal is likely to increase morale for those who want to stay, both by showing them they have the ability to stay, and getting low morale people out the door.

Perhaps because of increased productivity with LLMs, especially for developers?