i guess more cores//transistors/and..if i remember my electronics (your better than i) more transistors stuffed on the cpu wafers..and impact of 'gate lengths' and jolly old laws of physics.
Yes, though newer silicon geometries are getting around the expected limits. There was a time only a very few years back when they reckoned they'd hit the limits of small geometries because the energy loss through leakages exceeded the energy loss from operation. We've passed that 'limit' a while back now.
Physics still says "not so fast" fairly regularly.
"Gravity isn't just a good idea ... it's the law!"