It does though. Like why waste time if you know a viral GPL-style license or a patent encumbered license would be a no go?

This is akin to saying SWE’s don’t need to understand GDPR, COPA, HIPPA, DMCA or whatever. Obviously there might be cases where someone never touches code in a GDPR or HIPPA context. But any SWE working in those areas should damn well understand the basics of the law — at least enough to flag inadvertent, but none the less blatant violations.