Merrill Heatter probably knows, but is he saying anything?
Seriously, if I had to guess, I would say that what made the Gambit Board good in the CBS version was the unusual prizes (a trip somewhere on your next anniversary, tickets to various football bowl games, a game of 21 against "the house" for $2500), which they didn't have on the NBC version; the bonus round was stale. Plus, switching to the Big Numbers upped the prize from $5000 plus prizes (and whatever the Gambit Jackpot was at the time - usually $1000) to $10,000.
