What determines the frequency of network cable
The “ratings” you are talking about are mostly marketing claims by the manufacturer. Both cables have worse attenuation and crosstalk as frequency goes up. One cable was tested to 250 MHz, one was tested to 500Mhz.  Perhaps their performance is similar.

The cable manufacturers can improve the cables, but it costs them money. For example, although both cables are “gauge 23”, the lower attenuation one may actually use slightly bigger wire.(there is some slop in the wire gauge spec).   Perhaps the surface of the lower attenuation wire is smoother than the higher attenuation one. Losses in the dielectric can be less in the better cable, due to better plastic. 

Also, by winding the twisted pairs more carefully, crosstalk can be reduced, but then you need more expensive manufacturing. 

Anyway, short answer is cables can be and are better or worse, but there is also a lot of marketing hype in the twisted pair cabling business.