They know we like shagging them, its a control measure & a bit of a power trip, my ex-Wife, tried this on me on many occasion it normally lasted 3 day's then she wanted a cuddle, I used to give in but I got my own back by no cuddles, extended Bar time & the return to wkends on the hills or surfing. (and then shagging surfer girlies)
Also she used to nag the life out of me .....so i binned her 8)
The trick is to make her think you don't give a shit. Most blokes f'uck this up but if you want to get your mrs to put out more you need to make her think she has to chase you. It's easy for wome to get sex, wether they are single or in a relationship. all they need to do is say yes and lie down.
Try this on your mrs. Stop making advances on her for sex. Act like you aren't really bothered if you have sex or not. This will terrify her as she will wonder what the fuck is going on and be worried you are losing interest in her or are no longer finding her attractive.
When she thinks she has you she won't need to put the effort in. And women seem to get more of a buzz off attention, or knowing they have power over a man than they do actual sex.
Most blokes fuck this up though because it takes a few days of not coming on to her. Patience will be rewarded.