Why isn't Wrestlemania the best ppv of the year every year?

When's the last time it actually was the best ppv of the year? That's another question I have cuz I've taken some years off from wrestling and I've yet to see it. This year is a perfect example. Extreme Rules was clearly a better ppv. They promote Wrestlemania so heavily and then most of the matches seem to be just another match in the middle of a fued instead of the culmination of a fued. Punk and Jericho were definitely saving their best for the last match of the fued which ended up being Extreme Rules. The result was just a pretty good match. Is that what we look foward to at Wrestlemania? A pretty good match in the middle of a fued? What the hell are they going to do if Undertaker can't wrestle anymore? Instead of putting together the best ppv of the year, it's one epic match featuring Taker and a bunch of other stuff that's just ok. Really? Is that what Wrestlemania is supposed to be?