I have the most current iTunes (v12.2.1) on OSX Yosemite (10.10.4 (14E46)). I have been experiencing the same problem, so I tried the solution provided.
There is no 'Store' menu at the top of the screen in iTunes. I tried the above steps using the 'Account' menu instead, but even holding down the option key and clicking 'Account' didn't make the iTunes Match selection appear.
If I click on iTunes Store link on the iTunes screen itself, iTunes Match appears in the menu down the right side of the page. If I click on that option, a screen appears and asks me if I want to authorize my computer (like it does when you first sign up for iTunes Match). If I click that option, it fades out that button, but stays that way and does nothing else. Otherwise, if you go to my account itself, my computer is, and has been, authorized all along. Not sure what else to try. Thanks.