I often wonder why men (it seems) only come to this conclusion after there are issues? I mean really shouldn't this have been done from Day 1 of the marriage.
It almost seems as if a lot of men follow the same script. Bomb (after the shock) they go into Super-Father/Super Husband mode.
"I'm going to make dinner. I'm going to do the dishes. I'm going to spend more time with the kids. I'm going fold the laundry. etc."
"I know it gets a little tricky if the W is a SAHM, but there is still stuff to do."

The problem comes in because of personal expectations of the other....If their is a communication or understanding problem in the marriage, this will lead to frustration, disappointment, anger and if it gets bad enough DIVORCE

"It it any wonder why the Ws doubt the changes. I know everyone promises to keep them going and I'm sure many do."
It takes consistent actions over a period of time for anyone to make changes real.

but why does it take the wife leaving to trigger this.

People really only CHANGE for 2 reasons. Too much Chaos or FEAR OF LOSS. It got too chaotic so she changed her mind and wanted out of your marriage...You lost her and you changed and want to do everything you can to save it...simple really
Many lbs should understand that turning the FEAR of LOSS back onto them may be the ultimate answer to get them back.

I don't want to suggest that if you only helped out around the house, you might not be here. God knows there are people here who did do their share and are still here.

Exactly right... Plenty of NICE guys and Doormats are the ones getting divorced

Honestly, a part of me is embarrassed by this as a guy.

well sure, we all fall into ruts, act in ways that we later regret and take things for granted.... But this is what learning from your past, living in the present and looking towards the future is all about.