Because recruiters can reason about the latter but only engineers/practitioners can really reason about the former.

Non-degreed applicants almost always need a recommendation to bypass recruiter screening (though recommendations work better than recruiter CV screening in general).

The point is who says you are accomplished and your work has an impact? For coding,yes. Your github account showcases your accomplishments and it is open to everyone for verification. But for the rest, i mean the non programmer jobs in sales, marketing, retail,finance ,customer care you cannot have your accomplishments showcased in a verifiable manner. For any company or recruiter, a guy from a decent college with good enough grades gives far more comfort than a random guy with a blog.