I recall there was at least one poll that gumdrop made public where he asked patrons which route they liked better and I think it was meant to be the focus of future releases. The mom+son route won, but just barely (like 55-45). Two questions were folded into one, which route they liked better and what to focus on, so people may have mis-voted.
I think a lot of patrons hold out for the virginal daughter, but they also liked the son route better because there's actual conflict there instead of the sugarcoated dad.
My memory is hazy, but I think that after that poll was in was when he started getting lazy.
Just for the kicks, a little crazy theory.
Note: I only played a couple of first acts and then just extracted graphics for the eye candy, so I may be way off base here.
It's clear the father half of the game has been given more attention. But the father is sugarcoated, he's perfect and faultless. The daughter adores him.
It's as though Gumdrop only wanted to work on the father+daughter route and wanted an excuse to abandon the son part of the game.
Since the son half of the game was given less love, both the son and the mother are less likable as characters, but their story actually has more drama.
When playing as father, you mostly interact with your daughter, and later with the aunt and niece. There are no interactions with your son or your wife to speak of.
But when playing as the son, you get to interact with the mother and with the daughter which is when you (are supposed to) realize the daughter is so much nicer than her mother and the son is (supposed to be) a douche.
Funnily enough, the end result is that you're more invested in the son's story and want to see how it develops because it actually has potential to surprise you (as opposed to the run of the mill dad route).
Maybe Kyle went through a messy divorce himself, has no children (so has no idea that you generally don't go around fucking your children) and wanted to work out his own issues in the game but when he achieved that goal (and made a ton of money in the process), he lost all interest in it?
That would explain both why he lost interest and why the dad route seems very personal, almost intimate (dad is proxy for Gumdrop), while the son route is so detached?
(Or maybe, the guy does have a daughter, fucked her and is now realizing it was sick.)