"Free beats" is a gimmick. Just like any business that gives out a free product or service to bring awareness of their product or service.
So this is the main reason people give out free beats.
They are trying to build their email list to market there beats through emails or to get content-id revenue from the videos the free beat downloaders upload to youtube, and some are even hoping someone uses the beat they allowed you to download for free in a song that blows up so they can sue you.
What most producers don't tell you that if you make any money off the beat you can be sued. If you upload anything that has the beat that you downloaded for free to youtube, they can claim your whole video.
It's really simple for artists or content creators.
If you want to monetize anything with a beat that you downloaded for free you will need at least a leasing agreement or ownership of the beat to make money legally.