I've said this before, and I'll say it again. I really think Triple H's disdain for Jericho stems from him perceiving Jericho as a threat to his spot.
When Jericho was a top heel, he beat Austin & Rock in one night (something even the H's hasn't done) and he was definitely accepted by the fans as a legit top heel.
Think about that for a moment... how many guys has WWE had besides HHH that have been a successful top heel in the past 5 years? You can probably count them on one hand.
Austin's heel run went completely awry, and Rock's hollywood heel run was marred by the fact that he wasn't around to develop his character in the way he did as "Corporation" Rock. Taker's heel run lasted only a couple months, and he was nowhere near the level of heel he was as Ministry Taker fighting Austin.
So, what does that leave you with? Edge? Whose heel heat seems to be mostly generated because people like Matt Hardy, not because they dislike Edge's character so much.
Orton has been an utter failure as a main eventer. The guy has what, 4 straight wins over HBK now, and yet I still can't take him seriously as doing anything but keeping the belt warm for HHH.
JBL? I'll give you that one, as JBL was a solid heel on SD, and had a good run with the belt that very few people actually saw. Plus, as Heyman said JBL was only holding that title because HHH wanted to take Tuesdays off.
Big Show was laughable at best as a top heel, since he lost all the time. Which, of course, was unbelievable as the man is 7ft and over 400lbs.
What's that leave you with then? Three guys? JBL (if you count him) and then Brock and Kurt. Brock and Kurt, who "coincidentally" were both moved over to SD and kept off HHH's show for the most part.
Call it what you want, but I really think a lot of the reason Jericho hasn't been pushed properly is because HHH knows damn well he's expendable with Jericho at the top of the card.
Think back to how crazy the people popped when Jericho "won" the title in the opening match of Raw 6 years ago. That was insane!
Let's look at some other potential factors too: Jericho is a WCW guy, HHH has always looked to bury WCW guys. With the exception of Big Show, who I believe got depushed mostly for being too lazy, guys like DDP, Booker T, and even Goldberg really didn't get a fair run in the WWE. Yes Booker, Goldie, Benoit and Eddie all got shorter title runs, and I give WWE credit for doing that. Still... I'm sure had the brand split never taken place those title reigns would have been much less likely to take place. Save for Goldberg's who was too big of a name not to chance putting the strap on.
Plus Jericho is a bit of a tweener. Vince and HHH love their men big and bulky. If you're not at least 6'4 (with lifts) you need not apply for the role of extended WWE champion.
Meanwhile WWE never hesitated to push their own talent even when it didn't make sense. How else can you explain Cena, Orton and Batista's repeated title reigns? All very long, all very flawed, all very bitter for the fans, when wrestlers like Jericho are on the roster.