Body shapes

Most mobile devices have a space between 8-32 GB and a RAM of 2-4GB

Most devices would not be able to accommodate these kinds of changes, the game would become too big

Newer devices can have 128-256GB  ($500+ for 128GB, $700+ for 256GB)) and could probably handle it but then everyone would be forced to get these new devices if they wanted to continue playing and even then the number of apps you could have in addition to the game would be very limited

The sims on PC, Mac and consoles have these options because they have much more space, better graphics and so on

For $700 you could get a good computer so you can play the Sims, and have a high degree of customizing your sims, for $400 you could get a console.

Yes it is a different, more free style game, not as structured and it costs money to download but please understand that the free versions of the Sims on mobile needs to be simplified in order for it to work on the mobile devices. If you want to play a complex game (with lots of customization, bigger worlds,seasons and different options), mobile gaming is not the best option, you'll need a console or a computer for that.

I use a bit of a workaround for this.  The clothing styles give Sims varying size and shape to some degree.  The plain female adult tank tops, for example, make the Sim appear quite thin, and the long sleeved blouses or button down shirts have no waistline definition.  Same with the bottoms selection.  I know it’s not even close to what you are requesting from EA, but I find I can have somewhat different sized Sims by clothing choice.