companies that collect their laptops from laid off => where do these laptops go? how they recycle them?

It's a huge "depends". Different areas have different recycling opportunities. Some hardware providers have their own buyback/replacement programs. Also some companies may want to reimage and reuse the returned hardware. Finally you want some stock of temporary laptops available for people who are waiting for repairs so some functioning used ones are great for that.

Redistributing them to new employees/interns is very common, especially if the laptop is only 1-2 years old.