Well some of your questions have already been answered, but let me take a crack at this.
I suppose there’s a lack of ‘rules’ towards including personalities, ideologies, goals, religion, and backgrounds is because… well… they aren’t really seen as important as gender, romance, and ethnicity in the CoG forum crowd.
The key words here being “as important” and “CoG forum crowd”.
If you browse Steam reviews or Google reviews of IF games, you’ll find a very different reception to what forum goers prefer.
Another possible reason these things don’t have rules is because they’re not commonly included in an IF. Speaking from a coding perspective, it’s hard to crunch down a personality into a number or a percentage and even harder executing it to be worthwhile in a game.
Most of the times personality stats are usually fluff or just provide flavor text in a game. And what I mean by ‘flavor text’ is that if you are 70% Sarcastic then an NPC might make a snippy comment about your snark maybe once or twice.
A lot of the character customization choices (ethnicity, sexuality, gender, etc.) are static, surface level even. They don’t mean much in terms of gameplay except to maybe affect the romance aspects of a game, if the author chooses to do so.
And… I say the coding gets as complicated as you want it to be, in relation to character customization. If an author wants to make a variable for the MC having vision correction and then do a classic Scooby Doo gag and have their glasses knocked off, then they can go for it.
It’s entirely up to how much effort the author wants to put into the game and its variables.
As @Eiwynn said, you don’t have to do X or Y in a game. You could end up writing and then go onto publishing your IF in an entirely different publisher instead of CoG if you wanted to. But CoG, the company, has varying requirements, depending on which brand you submit your work to.
To answer your question about inclusive heroes over elderly, ugly, etc. type heroes, I would say that it’s what’s popular. Most people don’t really like slice of life, under dog stories in their IFs since IFs are primarily escapism fiction.
To answer your other question about why it’s strange that settings remain static despite swapping gender or any other choices, it’s - again - escapism. Pure and simple.
Besides obviously inappropriate story topics, the world is your oyster.
You can write a preestablished character or write a blank slate one. We have a few very successful publications where the MC is an established character.
You can choose to have the most detailed character customization or just the bare bones customization. It’s up to you.
When in doubt if you have questions or comments or concerns about your work, just ask your readers or ask around the forum and you’ll get answers. And from there? You can make an informed decision.