I mean, I'm trying to create some standard size chip cap and res footprints but I see that I should specify the size of the component, but 0805[2012] is 0805[2012] so why isn't there an option to just generate that footprint with one click? Or is that option there and I'm missing it?

The various types such as Resistor, Inductor, Capacitor, Diode all the different 3D model shapes. 

Different vendors have different terminal lead lengths and different package tolerances. All of these impact the resulting pad stacks. 

Bottom line is that the Footprint Expert cannot throw out random dimensional values, 

Here are some sample Chip Packages of some random parts -  uploads/3/CHIPS.zip" rel="nofollow - uploads/3/CHIPS.zip

It is possible to create a generic 0805 footprint that will work OK for almost all parts, but you need to do so with care, and you should check it against every new component you use it for.

"0805 is 0805" is not a true statement. For instance, the popular Vishay CRCW0603 and CRCW0603...HP resistors are not the same size, and both are narrower than the Panasonic ERJ-3 series. Terminal sizes and gaps vary significantly.

A generic one-size-fits-all footprint will naturally end up larger than usually needed, which impacts placement density.

You can create on 0805 Footprint for each component family by using the same dimensions and tolerances. 

Height is the only value that will be variable, and it will affect all the 3D STEP models. 

Then you think you will just use the worst-case Height to cover all 0805's but the variations are really different between component families.