Not saying Mom or any variation of it

Anyone else's toddler refuse to say mom? My son speaks pretty well, recites number in order back and forth, knows alphabet and identifies letters, says dad and sisters and even calls his sisters by name (Soli and Lily), but refuses to even try and say mom. I know the M sound is not the problem as he says milk clearly. I am a stay at home mom and with him every day. Does he just not feel he needs to say it? It just makes me feel kind of sad that i have never heard him say mom, mommy, or anything even close. Tell me others are experiencing this, as I never had this issue with my girls