Well, not deliberately, of course not. But after having lost 2 or 3 matches, I expect on a subconscious level at least some of the players will have come to the conclusion that the glory isn't going to be found in winning the 40 over competition this season and so their performances have dipped...
Having scored 330-odd in the previous match and lost, I'd imagine Sussex were somewhat fired up for this match and the pressure was off with Notts expected to win. Sussex are still decent in this form of cricket, albeit their priorities lie elsewhere this season.