I can’t believe nobody has answered this question yet.
I can tell you exactly why your wife does this.
She does it for the exact same reasons I wear a suit to nice parties, but don’t wear a suit to bed.
See, when people go to parties, they wear nice things, and a lot of women enjoy wearing what you call “revealing dresses” because those dresses make them feel sexy, and every woman enjoys feeling sexy when they’re out.
See, a lot of women have issues with the way they look, or body issues, or self-esteem issues, and if they can put something on and feel attractive, or feel sexy, then they’re more confident in public, and they’ll have a better time. They’re not wearing those sexy things for anyone other than themselves, regardless of what you think, unless they are, which is also fine.
But when women, and literally everyone else, gets in bed, they want to be comfortable more than anything else. Your wife assumes that you love her for her, and that you don’t care what she wears in bed or otherwise. That should be the case.
So when she gets in bed, her first concern is going to be comfort. She might put on a soft pair of cotton pajamas, or some shorts and a soft shirt (like my wife), or she might just sleep in her birthday suit.
Whatever she chooses to wear, she shouldn’t be concerning herself with what you think about how she looks. She should be trying to get comfortable to go to sleep, so she’ll sleep as soundly as possible.
And let’s be realistic: if you want to have sex with your wife, does it really matter what she’s wearing? She could be in a dirty track suit; it doesn’t matter. It’s coming off.
I hope this has been eye opening for you.