If you watch the NIT teams play, you will notice the ambivalence of the participants.
These are no more than exhibition games and almost zero fan interest outside of the schools participating. The trend will continue to decline invitations because so many players are either graduating or entering the transfer portal. Zero development is taking place for most players.
Schools like St. John's, Memphis, Syracuse, Oklahoma, etc. no longer see any financial benefits in participating.
I don't know how long of a contract there is to hold the NIT but I predict it will ultimately be folded into the NCAA tournament.