It's a yield thing. They have to be binning as loose as possible so most chips that actually end up not having any defects end up as the 1065G7 and the remainder as the 1035G7. And so on and so forth. That's part of the reason the 1068G7 and the Icelake-Y models never got released (until now/soon)... they have been stocking up the 1% for them.At the end of the day, that seems to me to be the biggest failure of 10nm; it doesnt appear to be any more power efficient than 14 nm. One could live with the lower clockspeeds in mobile if there was a good power savings that allowed running at sustained higher speeds, but it just doesnt seem to work out that way.
If yields improve you will see things get better in that front with Tiger/Alder.