Vanilla- I think partially he was embarrassed and uncomfortable to spend that much money on himself. At the time I earned more than twice as much as he did and we had just purchased a home exclusively using money from my stock options as a down payment. When we met he was just coming off a period in his life where he had gone back to school - so while he was employed - he was just starting off again - while I was pretty far down the career path.
I think this was another slow poisoner of our marriage. He always felt a bit like the junior partner although I certainly didn't see him that way. We actually did have a real, meaningful conversation about it - where I pointed out how unlikely it was that I would continue to out earn him in perpetuity. (Being someone who loves statistics-I pointed out to him that as a woman, I would end up earning less than him over time for a variety of factors). He did seem to take some comfort from that.
He was always a little erratic in his logic on this subject though. Until he became a cop - he jumped around from job to job although he was always employed. He didn't want to get married until he had a solid job with a future. He got it and celebrated the first day by saying "We can get married now!" and then quit it two months later because he hated it (we still got married). Then, once he got into law enforcement, which he has a real passion for, he repeatedly turned down promotions because he didn't want to deal with managing people and all that paperwork.
In the meantime, I let my career stall and started taking on positions with fewer responsibilities primarily because I didn't want to be working 60 hours a week with small children. However - in full honesty, I did view it as an additional benefit that I wouldn't earn so much more than him. It was the right decision for me because of the kids - but its pretty easy to second guess right now when a higher salary would be pretty helpful, to put it mildly. But I have no doubt I'll get back up there again.
The irony in all of this - is that about 2 months into the separation - he completed his probationary period in his new job and a bunch of raises kicked in- so for the first time he makes close to the amount that I do. If he continues on - he will be making an excellent salary in a few years.