Unless there is a meltdown, the ACC teams that will make the tourney this year are: WFU, Duke, UNC, Clemson, and Miami. That is 42% of the conference. Anyone remember when it was a regularity to have 44% of the conference in the Sweet 16 (much less getting invites)??
The reason only 5 will make it is that there are only 96 wins to be had in ACC conference play. If the top three teams beat everyone else, then there are (16+14+12) about 42 wins taken by the top 3 teams. The fourth place team is bound to win at least 8 games, so that takes us to 50 wins to split among the other 8 teams. If the fifth place team (Miami) wins 8 games, then we only have 38 wins to split among 7 teams. In that situation it is extremely unlikely for any of the remaining teams to get even 7 wins, much less the 8 normally required by the NCAA selection committee. If Miami or Clemson somehow fall apart and only get 6 or 7 wins, then we are likely to have a cluster of teams in the 6-7 win range, assuming that NCSU and Georgia Tech win around 5 league games combined. In that situation the league will once again only get four invitations (33% of the league, an all-time low).
The bottom line is that when a few teams at the top win most of their games or the bottom of the league wins a handful of games, the middle of the league suffers. Whether or not that makes for a strong league is not the really point. It is incumbent for this small portion of the league to do well in the big dance (that means you Clemson, Duke, and Wake Forest, the teams that have recently no-showed in the tournament).