Some coaches like Matt Rhule have pretty openly stated that their motivation for not having a Spring Game is that it's basically an invitation for other programs to scout their 2nd and 3rd string guys for young talent that's on the bench and then have the collective pitch some N.I.L. offers immediately afterwards based on what they see in the scrimmages.
The timing of both of the transfer portal windows created by the powers-that-be has left a lot of coaches frustrated. The winter portal basically forces guys to make the decision before bowl games and playoffs, and the spring one seems to be creating a disincentive to have the games.