Never really looked at this before but quite interesting. Why for example under 'multi core' would recent MacBook pros absolutely destroy everything except iMac pro/Mac Pro? Whereas single core it's much of a muchness.
Similar to what Aggi said.
Long story short, recent cpu development has been all about power efficiency and increasing the number of cores.
For ages then processors just got faster by running higher clock rates. Hence you got Pentiums 4's from 10-15 years ago being overclocked to ~8GHz.
But temps were always too high so everything moved to multi core because it's far easier to run 2 cores at 3GHz than one at 4.5GHz (for example). The architecture and instruction sets got more sophisticated too so it's not just speed and number of cores.
So you'll see single core performance hasn't continued the upward trend anywhere near as much as it did, but multi core has continued to improve.
The only problem then is developing programs to utilise multiple cores efficiently.
(Assuming no other bottlenecks) 5GHz is always twice as fast as 2.5GHz, but 2 x 2.5GHz is almost never twice as fast as 1 x 2.5GHz