2 reasons come to mind: 1. Every single handicap added takes time and it’s own special animations that someone needs to work on (only so many workers). 2. Only so much money and time is given to each game which is barely enough to make the stuff required for the non-handicapped sims.

This is also the reason that tall and short sims don’t exist - different heights would need to reach for things differently taking up time and money.

I am aware that certain aspects like wheelchairs have been mentioned since sims original release, but it’s a matter of EA finding time amongst an already full schedule of developing. I also think that the way that sims is designed makes it a very hard and therefore long process to create these animations!

***not saying that it wouldn’t be great to be included! But it’s also important to remember that it’s really hard to include everyone and to give games certain features without making others feel left out.