For new cars, most of the settings in sims boil down to "set it and forget it." Have never felt the need during an AC SRS race to monkey around with TC or ABS settings. G29 often has more than enough buttons even for intricate stuff like KERS, DRS, or hybrid management. Half of our sims don't even have rain or night time racing so why TF do I need to map extra buttons for wipers or lights?
That's a strange opinion with current sims. While I'm certainly not a very gifted driver, even I have to use a lot of the controls especially in endurance races in ACC. I will need to change TC, ABS and brake balance during the stint because otherwise my talent would run out pretty fast. And that's without weather changes, add that to mix and I will need a lot of additional switches from lights, wipers, engine map and so on.
You may be right for just 20min quick races, but as soon as it gets a bit more serious more buttons are extremely helpful.
Also I like to use my button box on different game genres like ETS2/ATS, ED and x-plane, it's quite versatile all around.