It might come down to the choice of being a big fish in a little pond vs the opposite. I seem to remember Parker dipping his toes in the water at YR in the 90's where he was just average.
That was part of it, but it more had to do with his safety and sobriety at the time. He's had a pretty tough life, losing siblings, having another born deaf, and eventually losing his wife who was a major factor in helping him get clean and sober. He had a major drinking and drug problem and went away for it. When he first started at Yonkers he was dipping his toes, which you really can't do. Either you're in or you're not. More importantly, he was just barely clean and sober. He was still getting his sea-legs under him. Linda Toscano wanted to use him on everything as she still was NY based. He just wasn't emotionally ready. He wasn't shaking hands, chasing business, etc. Larry Summer used him a lot and after a while he was doing very well there. At the same time, he was getting courted by some trainers at the Poconos. Then he got a bad suspension on a "lack of effort" drive at Yonkers, and Faraldo tried to turn it into some major constitutional law issue. All Zeke wanted to do was stay clean and sober, and drive. However, by the time he left was very competitive and one of the top drivers there. He just wasn't happy. He only knew happiness with being simple, and simple was him being in Monticello.
Personally, I believe Zeke had the ability, the talent, and the skills to not only be competitive at Yonkers, but to dominate there. Same thing with the Poconos. It was never a question talent, ability, or skills. Not for people who know how to judge and rate a driver. It was a question of his emotional state, well-being, and the timing.
Palone got voted into the HOF because of all his wins AND what he did on the grand-circuit competing against the best, on a national stage. Parker never did that.