This is very common. I can think of two possible explanations for it off the top of my head. The first is that your wife just has a particular level of affection that she wants in the marriage. If you're doing all the work to provide it, then she doesn't have to do any. It's like you're Chester and she's Spike.
When you pull back, she is willing to fill the vacuum. It satisfies her, but leaves you unsatisfied because your preferred level of affection is, perhaps, twice hers.
The second possible explanation is that your wife feels too comfortable with your relationship. She feels like you will accept anything she does without ever leaving her. That's a dangerous attitude for someone to have. It leads to taking one's spouse for granted and not seeing the need to meet that spouse's needs. When you pull back, she begins to worry that you may, indeed, leave her. This may be a subconscious thought process. But, she realizes that she needs to pull you back in. So, she steps up her game.
Sadly, this is a game you need to master in order to have a satisfying relationship with the majority of women. As another poster said, your wife needs to feel safe being sexual with you. And, she needs to feel unsafe not being sexual with you.

When you pull back, she is willing to fill the vacuum. It satisfies her, but leaves you unsatisfied because your preferred level of affection is, perhaps, twice hers.
The second possible explanation is that your wife feels too comfortable with your relationship. She feels like you will accept anything she does without ever leaving her. That's a dangerous attitude for someone to have. It leads to taking one's spouse for granted and not seeing the need to meet that spouse's needs. When you pull back, she begins to worry that you may, indeed, leave her. This may be a subconscious thought process. But, she realizes that she needs to pull you back in. So, she steps up her game.
Sadly, this is a game you need to master in order to have a satisfying relationship with the majority of women. As another poster said, your wife needs to feel safe being sexual with you. And, she needs to feel unsafe not being sexual with you.