I assume that Copilot uses open source projects on GitHub to “learn” what to suggest. Some of these projects might be under, say, GPL v3. A developer uses Copilot for a commercial project and Copilot insert a complete function from a GPL v3 code into this project. Someone notices this and sues the commercial project for breaking GPL v3. Will GitHub pickup the tab?
a person bought a hammer/knife from a shop and used it to hurt another person. When the victim sues the attacker, can the manufacturer of hammer/knife pick up the tab?
But being digital, the knife was just copied and the original owner still has one, but you also have theirs without their permission. So there's much less sympathy for the victim.