People are looking at it wrong though.
With Undertaker, yeah people have lost streak matches and it didn't hurt them, but this was before Undertaker left after Mania and people were stuck on the show with their tail between their leg. Edge had beaten Undertaker several times before their Mania match. Batista got to feud with him and have draws and look good against him after their Mania match. Same with Henry and Orton. And prior to Orton the streak really wasn't what it was. Then in 2009 the Undertaker wrestled Shawn and left after Mania and didn't come back until ironically the time he wrestled CM Punk after his heel turn. Shawn also was gone after that Mania. Same thing happened the next year, and guess what, Shawn retired after. After that HHH layed Taker out at Mania 27 and he was gone until the next year. HHH was gone after Mania too until, again ironically, HHH came out of retirement to beat Punk when he was hot and then go back on sabbatical until Mania. Then they both repeated that. Then the year after Punk, Lesnar beat Taker, and he wasn't left and didn't even use the heat from it until SummerSlam.
So no Punk was the only guy who wrestled Taker while he was part time, and wasn't a partimer himself. He was the only guy who jobbed to Taker and had Taker not around to feud with after the big show. And keep in mind in 09 and 11 he was white hot and a guy came out of their rest period post a Streak match and beat him, cutting out his legs.
Punk is unique in that.
Now lets move onto Rock. Miz and R-Truth lost to Rock and Cena, but they were glorified midcard heels losing to the two biggest babyfaces in the company. Cena lost to Rock, but it was part of a giant 3 year program to put Cena over. CM Punk was a main eventer, he turned heel to face the Rock. He sacrificed merchandise sales to be a heel for that. Rock got to beat him twice, Punk never generated heat again, Rock loses to Cena at Mania, Punk loses to Undertaker. Bot guys are gone, and Punk turned heel and took to big losses with both guys out of the picture to even salvage something storyline wise. He got the short end of the stick.
Now lets move on to Brock. Cena beat Brock. HHH traded wins with Brock for no reason. HHH gets to leave and take a break off camera after his first loss to Brock. Then he gets to beat him. Then loses again and takes another break. Punk has to lose to Brock, and THEN Brock goes and Punk is once again left on his own with a loss in a major program, on his own to salvage something of his persona out of it, since that loss Punk was stagnant in the company until he left. Really go back and watch that period, Punk lost a lot of momentum from that.
Now keep in mind these all occurred at the Royal Rumble, WrestleMania, and SummerSlam consecutively. So at the end of this Punk was left in the river without a paddle, and the light at the end of the title was some midcard match at Mania against Triple H after him doing nothing for 6 months. Now add the injuries on top of that. Now add every other issue he had from that period from Vince shooting down his ideas and giving them to HHH, HHH not respecting him and not so much as giving him a call when he lost a movie role. Add that the dude was working the crazy Cena style main event schedule to prove himself for some reward they had no intention of giving him. Add the frustration we all had watching the Batista debacle and the Daniel Bryan depush last year before they finally got behind it the right way. Add in the fact that this dude wanted to leave 3 years ago and only came back because Vince begged him and swore things would be different. Add in that nobody was talking about how the network would effect ppv payouts. Add in that fact that Punk's a big enough name to have a real career if he left.
I don't blame him for feeling the way he did. He didn't do anything wrong. WWE has their stupid independent contractor thing so he could quit whenever he wanted. Which by the way, he's right, it's completely illegal and WWE would lose in a heartbeat if anyone sued him on it. Then their entire business model would be screwed. Then WWE tried to withhold royalties which they made based of his name. These aren't exactly new things that people complain about.