Why doesn't any of the Instant Pot recipes I find use the preset buttons (Rice, Bean/Chili, etc.)?
For the most part, the buttons just have pre-set cooking times.  For other times, then it's best to just use manual modes.  A few of the programs are particular, like the bean, multi-grain and porridge programs have a long pre-soak before pressure cooking.  And newer models (SMART, DUO-ENW) have the rice program pre-set to cook at "low" pressure.

Instant Pot made nice little charts of these programs and posted them online.

In my personal experience, the extra soaking time of these programs just takes longer - especially if you're already using pre-soaked beans. 

That's why I always use manual mode - and the recipes I wrote for their recipe booklet always call for it as well.