Why aren't Forever stamps sold in Rolls?

Probably because if it were too convenient to stock up on them at today's prices the projected future $$ losses would be too high. So..to temper this they knock down the convenience factor a notch or two. They trying to strike an acceptable balance between making money now from the gimmick of a stamp that is good forever and "losing" money in the future when postage is twice as much as the forever stamp was purchased for.