Says who, other than you? And by what standard are they worthless? That is simply your declaration. Who put you in charge of that judgment that must be accepted?
Until the early/mid-1960s, the NIT was more prestigious. The NCAA had to pass a rule demanding that a team accept their bid vs an NIT bid, else they could not play in another post-season tournament. In the 1940s and 1950s, the NIT was played in NYC vs the NCAA is other cities. Which tournament got the most media attention? Here's a hint: when Loyola of Chicago won the NCAA in the early 1960s, the game was not even shown live in Chicago let alone elsewhere. Like it or not, NYC is the premier media center in America.
Why is 1939 the cutoff? On what basis is this determined? If you are going to claim that it is because at that point the national championship was decided via tournament, then wouldn't that rule also be applied to other sports? If so, then all those football championships that Texas, Oklahoma, Georgia, Alabama, Minnesota, PSU, OSU, USC, ND and Army won prior to the BCS creation (and which were all voted) are no longer viable and therefore do not count? Try selling that claim to those schools.