Free personal tier is basically a cheap advertisement for them. You try Tailscale personally and get used to it, then it is very likely you would want to deploy it at your work seeing the benefits scaling even more with more people. And then they make money.
1000%. Tailscale is the first VPN I've used that makes my life easier, and I'm using it for personal access to my selfhosted servers at home. I will definitely recommend it to companies I work for in the future.