I think devs tell themselves this when it's not true. Milfy City being a prime example of a game with plenty of mom sex scenes, yet has a rabid fan base so desperate for more content they've been waiting for over a year for an update.
If a game loses its audience after the mom sex scene, it's because it's a bad game that had nothing else going for it. Not because of something as ridiculous as a bad audience.
If anything, Devs should respect that artificially drawing the mom sex scene out can ruin a game. No More Secrets being a prime example of the dev fucking up the timing so bad that the eventual scene was this unclimactic, tawdry, out of the blue affair. Missing entirely the perfect scene at the hotel several updates prior, which he had ended with some bullshit blueballing. I'm also fairly certain the dev's passion for his project had died out by the time he finally crammed the scene into the game while rushing towards the end of his project. Which raises its own concerns about Devs delaying.
I actually suspect Midnight Paradise might be the next example of a game that has artificially delayed the mom scene for too long. Hopefully the scene will be able to justify the wait, but I sincerely doubt it.
Again this all hinges on the assumptions that
(a) the majority of the playerbase wants mom content more than other content, and
(b) Faerin intentionally delays mom content to keep supporters
The first assumption is false, the second unproven but probably false as well.
Okay, when I say the first one is false, I am mixing up "supporters" and "players" a bit, but since the update order is following Patreon polls which wanted the non-moms to catch up, at least the majority of supporters does not want Julia to be racing ahead. Whether it is because they don't like her as much, or because like me they like a "save the best for last" approach at least as far as "I don't want to have finished the pizza and be left with all the crust" way, or they abstractly think that a balanced game is better, we don't know. Fact is: majority of patreons did NOT vote for Julia when given the opportunity.
As for "what the dev does": only Faerin knows his plans. But from a development perspective, two approaches both have merits and we could probably discuss for weeks which one is better:
(1) Rush one character (here Julia) while completely ignoring the others
(2) Keep them balanced, especially when approaching "milestones" in game mechanics or similar
An intentional mix would be pretty bad for the development process. Of course, patreon strategic ideas could play a role - we would never know. But since he is also not a first time dev, and (my guess only) wants to continue doing games like these once MyMa is finished, he'll probably know what he is doing.
In any way, "artificially drawing the mom sex scene out" is a wrong description of what was happening here. Sure, we don't have vaginal with her yet - but we don't with any other girl as well. All while Julia had hardcore content way before others even showed their boobs. So that is not what is going on.