I may be misremembering, but I think they have said somewhere that Headscale is actually revenue positive for them.
That feels right to me. Headscale is mostly used by home labbers and small hobby users, it competes with self-hosted OpenVPN and WireGuard, not Pulsesecure, Cisco Anyconnect or GlobalProtect. It's a way to introduce Tailscale to people who love to try new shiny tech in their spare time, but don't want to give up control over their infrastructure.
Those people will then bring their Tailscale expertise and enthusiasm to work. Work really doesn't like managing IT infrastructure unless it's one of their core competencies.
Sure, some companies will actually choose Headscale over Tailscale proper, but I suspect that's a small minority (especially if you take company size and the money involved into account). That's just cost of revenue, not unlike Facebook advertising or billboards on the side of a road in Silicon Valley.