But some of us use long pant tights to protect from the elements. Cycling shorts are too bulky to wear underneath (because in the summer the bulk makes you too hot and in the winter the bulk can get saturated from freezing rain and give you hypothermia).

Plus, why go through the hassle of changing when you can just wear shorts which stay dry? If you spend 60 min commuting and 10 min changing then changing made you 15% slower...that's like the difference between riding a beach cruiser vs riding a ceravelo. Would you trade a $3000 ceravelo for a $150 beach cruiser? You might not care, but I personally don't like pissing away $2850 for no reason.