I was thinking the same when i was playing the game for the first time
I still hasn't finished the game even after few weeks , i am playing it slow for the best experience
I checked full save gallery and same thought , NO mom sex ??? why ???
but then I realized something and I want to share this point of view too
there are a lot of games in which you start with your home with Mom and Sis, you fuck them , complete their story and then roam around town for other girls/woman and completely ignore Mom after that and then finish the content... it kind of kills the build up , corruption (if the mom isn't already slut), and the reward for waiting and going bit by bit.
so if the mom has fast pace story and sex, while the the other girl in town do too( you fuck most in 1st/2nd meet) , whats the difference between both ?
the slow story for mom who is the most focused and loved character makes the perfect sense while the other characters are getting their story finished, we are talking about 30-35 girls with story and sex animation, all of it is hand-drawn which takes time, The Dev is sharing progress and listening the community and have a creative side for story and build-up.
so giving mom sex while other characters are getting their story isn't the desired thing, this game is not for quick fap and move on , it is a process , trust and enjoy ...