After being hyped as the "Culmination of Human Achievement", Infinity's brief track record has been pretty damned embarrassing. I mean before the vessel was even christened it was boarded by rebel forces and nearly hijacked. Then it crash landed on Requiem, and sure it scored a few kills on CRS-class light cruisers (lol), but it was boarded again. Then during the Requiem Campaign it did pretty well in space against an ORS-class and a few light cruisers, but then it got disabled and infiltrated again. Now against the New Colonial Alliance and some mercs it got pierced in an outright space battle.
I dunno if its gross incompetence or what, but hell, the Pillar of Autumn has a better battle record than Infinity. It was able to down a Supercruiser during the Battle of Reach, survived the bloodiest battle of the war, and scored three kills on vastly superior CCS-class battlecruisers.
So far Infinity has been shown to not really be worth half the UNSC defense budget for decades.