She doesn't have to, and nothing. It's just different and, to many, better/hotter in part because of the feel and part because of the taboo. Someone who loves their partner and wants to get them off should compromise in the bedroom.
Imagine every day you are given a plate with an apple and an orange on it. You are only ever allowed to eat the apple, never the orange, and any mention of the orange is met with a fight. You're told you will never get the orange, but you have to look at it all the time. On top of that, you see other people eating oranges and they all seem to love it! Don't get me wrong, you love the apple, but sometimes you just want to have a fucking orange and not an apple every day for the rest of your life.
My girlfriend and I went through something similar. I never pressed the anal thing and didn't even ask til we had been together for something like a year and a half. We tried it like 6 months later, and it went well; we prepped correctly, and from my point of view I didn't see any indication it hurt, in addition to her explicitly saying it didn't hurt.
Regular sex resumes, and a few months later I get her some toys, at which point she says anal felt weird/different and she didn't want to do it again. I asked if she meant 'never again,' and that's what she meant. I told her it was fine, I wasn't going to force her to do anything she didn't want to do, and not to worry about it.
Problem was, we were getting very serious by this point, in our late 20s and together for several years, starting to build a life together. A few months down the line I kind of realize that it meant I would never have anal sex again, ever, for the rest of my life if we remained together this way. I did not want that. I tried masturbating less, more, no anal porn, no porn at all, etc for months, but it didn't change how I felt.
After a lot of thinking (I didn't want to give her an ultimatum 'anal or we can't be together' as 1) I'm not a fan of ultimatums, and 2) I wanted her to do it because she wanted to do it/wanted to make me happy, not because I gave her an ultimatum) I realized I had to tell her as otherwise I would end up resenting her for it - she can't read my mind after all.
Thankfully, things changed for the better. And for the record, if my girlfriend asked me to do something I didn't want to do in bed (barring a 3rd person, neither of us want that), you bet I'd do it. I want to get her off and make her happy. OP's wife apparently doesn't care enough about her husband to change.