>>3246614That's not the reason. Every lens are made with special plastic inside because it's more tolerant to temperature changes and doesn't expand and shrink as wildly as metal does.
The real reason it the slim diameter profile of that new 28-75.
Once you have a lens barrel that is above 110 mm in length, you need a wider diameter to make 24mm field of view possible.
If you don't need that particular field of view, you can get a lens that is far smaller diameter, and thus far smaller front element and less weight.
