It could be cold damage from a rough winter. If the wood is dead it will not leaf out. Only thing to do is remove the dead branches.

I have a huge silver maple in my front yard and its noticeably sparse this year too. I thought it might be sick until we were taking a ride around the neighborhood and noticed ALL of the silver maples are like that this year. I was searching for answers and that's how I came here. I'm thinking it might have to do with the weather this winter. maybe not enough precip because I had no sap all over my car this year and last year I had tons if it. thanks for your question