NEX: Why can Sony do 28-100 pancake zoom on RX100, and can't make pancake for NEX?

Not expecting perfection... But if they have the lens expertise to make a 28-100/f1.8-4.9 zoom for a 1" sensor, why can't they build a similarly spec'd pancake zoom lens that is proportionately larger in dimensions for APS-C?

What are the engineering limitations that prevent? For the most part their pancake (16mm e mount) was reported to be kinda mediocre, and they have not made a pancake zoom for the e mount at all, so despite having the tiniest bodies and almost shortest register distance, they don't have a very small carrying kit body+lens.

Also, why are the fuji Xpro-1 primes so much better without Bein outrageously more expensive or outrageously bigger than the sony equivalents? They have the same engineering challenge (APS-c sensor and ~ 18mm register).

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Btw, I'm not ragging on Sony NEX. I just bought my NEX 7 and it shipped to my house. I'm getting the sigma 30/2.8 in the mail next week, and can't wait to play with it.

I just wish they had a pancake carry zoom & pancake primes to complement the rest of the lens line, or better native primes in general like what the Xpro-1 has.