He as written many useful books and identified a core set of principles for good design. That is much harder than being a cog in the building of a successful product.
That's an entirely circular argument and doesn't prove anything about Uncle Bob.
Question: Why should I listen to Uncle Bob?
Answer: Because he wrote a book telling you what to do.
He's got some un-controversially good opinions but he also has some opinions that are just plain stupid. Since his opinions don't compile and aren't testable, it's not easy to rate their over all value.
Are we sure they're good design principles? Have they been used to design and build something successful?
I think that's the source of consternation: he preaches, and has religious fervor, but what has his principle set built (even if it's not him doing the building!)? I honestly don't know the answer there...but it's definitely not obvious. It frames his arguments are 'just trust me', which rubs a lot of people wrong.
https://news.ycombinator.com/newsguidelines.html