He's gotta step back from his ego and be honest with his wife and family. It's clear he's about 4-5 years in with a larger firm. When he started, like all first years, he thought he was hot shyt. After 4-5 years, he senses from the firm that he isn't going to make it to 7 years and become partner and will probably be out within a few months. As such, he looks for any reason to use as an excuse on why he wants to leave his job before he gets let go for the new, shiny first year who is likely 60k per year cheaper.
Nothing but ego. While he was coming up in the firm, I'm sure he bragged and looked down on people who couldn't afford to let their wife stay at home. His letter screams "look at my job" "look at my house" "look at my smart wife". Now that he senses he's about to be let go, he's looking for someone to blame that's not him - in this case, its his wife. Pathetic.