Linux supports much less hardware than NetBSD.

There are entire categories of computers that simply cannot run Linux.

SPARC64 as an example in this very comment section.

Sure, but one is much more likely to have some ARM(64) SBC / smartphone / tablet / IoT device laying around than a SPARC box. Those are much more likely to have Linux than NetBSD drivers. Support for ancient architectures doesn't matter nearly as much as that.