Why does my husband act his worst during Ramadan?

Asalamu alaikum. My husband is Muslim, and every year when Ramadan comes around, he seems to show his worst side. For eleven months, things are usually fine, but during this holy month, he gets easily angered, yells a lot, and becomes more aggressive over small things. He doesn't drink alcohol and says he's trying to control himself, but his behavior is really tough to deal with. He isn't provoked, and I'm just confused about why this keeps happening. Why does this blessed month seem to bring out the worst in him? Just to add: my husband doesn't observe the fasts or offer salah during Ramadan. He never has. Yet, each year, his anger and aggression get worse during this time. I really don't get why it's like this.