Part timers sell PPV buys, and tickets. That's what's important to Vince unfortunately. The HHH vs Seth storyline should have been done and dusted by now, but it was put on the back burner for 4 months so the match could happen here rather than a B show, and they almost missed out completely because of Seth's injury.
I honestly could not care less about a main event than I do about Lesnar vs Goldberg, I cared about Miz/Cena (2011) more than I did about this. The story doesn't interest me at all either.
Taker is still a draw, and whilst he is able he will always have a spot at Mania, I have no problem with him showing up for Mania only, he's been a part timer for a decade now, but he's been with the company for 25 years and clearly respects the business and the company. He's earned that right.