He may not speak up about being a discontented house-husband (or about anything else he may be unhappy about) for the same reasons you don't speak up about things. Perhaps he doesn't want to sound whiney, pehaps he doesn't want to sound like he's backing out of an "agreement"...perhaps he's not even aware of something that is bothering him.
Here's something to think about.....you ask why hasn't he said something to you if he's unhappy....well, why haven't you said something to him? Chances are IMHO, that you both are stumbling into the lackocommunication blues so many of us have found ourselves in.
I'm really glad to hear you are planning a conversation with him. Keep in mind though, that this is just the beginning of talking about your problems....you are going to have to have these conversations multiple times. So don't give up if you feel you aren't getting through or that you are hitting a stone wall...just keep trying.
Also something to think about....How long are you willing to continue on in your marriage in the state it is in? Are you willing to continue? It's a tough thing to think about, especially if you love your H. But it does help you to come up with boundaries & consequences. Your H is going to need to know that "IF" this problem isn't addressed and we both work on it that XYZ will happen. Naturally, that XYZ consequence is whatever YOU feel you can enforce for his lack of attention or action. Make sense?