Probably because they were busy building those huge ground armies that made then some of the top-tier Clans.
WarShips are awesome, but in Clan space, 90% of power flows from the footprint of a mech.
It's disappointing but logical. They were trial based civilization that kept the combat to minimum, especially in big aerospace terms. You can't hold realistate with a warship.
Interesting enough the Wolves corvette was not unlike the Fox, but they didn't have the right mentality for it. At least fluff wise.
I have to say having being johnny come lately for the Blackpantslegion youtube/blog casts, i found his vid on the Tripitz Affair very interesting when comes to things about WarShips in the setting.