I think Udoka had a unique cred/aura. To me he had kind of an Uncle Phil/John Thompson presence the way he seemed to carry himself, despite not being that big (compared to NBA players at least), he just felt like an imposing presence.
Then there's his resume, not highly recruited, did the JuCo route and low-level D1 schools, As a pro, bounced around the minor and international leagues before finding carving out his spot in the NBA. He knows what it takes to grind and earn your spot. This can appeal to the non-star players.
But also played with and against Kobe, Shaq, Duncan, LeBron, Durant, Wade, etc. This can help appeal to the star players.
And then coaching. Coached under Pop, and coached Duncan, Kawhi, Embiid, Durant and knocked out LeBron and Wade's super team as an assistant.
Sure a lot of coaches have similar resumes (Kerr, Ham, Willie Green, Ty Lue, etc.), but they don't have that same imposing presence, IMO.
There's also the
legend of him single-handedly beating up an entire team by himself. as well as being tied down to a well known TV/movie star, that helps his cred too.
One thing that stood out to me is the the time Smart injured Curry. Steve Kerr is having a fit blaming Smart. Ime stone cold says Smart did nothing wrong. If I was a player, hearing Ime have my back like that would comfort me. Brad Stevens, Joe Mazzulla, Nick Nurse, Jason Kidd, Steve Nash, Darvin Ham, Willie Green, etc. could all say the same thing, but it wouldn't feel the same, they just don't have that same "authoritative" presence that Udoka had.