That's not unusual with s/w giveaways and that's how they do it.
Expand their user base, get more inquisitive people familiar with their product and state this only limitation (no support, no upgrades)!
Users may refer others to the product, either renew after the license ends or buy the product at a discounted rate (for enabling upgrades and support) from the same giveaway site - that offers a discount link immediately after the product giveaway period ends. Developers get more feedback and data too