There are many things in the GSL that I'm not exactly happy about, the primarily one being how you cannot reprint statblocks from the Monster Manual, which will have horrible implications on the presentation of adventures.
However, when it comes to the lack of "reuse" clauses for 3rd party publishers, I think they've got it right. This is pretty much how a lot of publishers - including some well-regarded ones - regarded the "Open" part of the OGL: Not for their products. Let's release "Crippled" OGC.
There have been exceptions, with Clark Peterson and his Tome of Horrors being the most shining star in that constellation.
For the purposes of this license, however, it seems to be the case that a large part of the OGL "community" has reaped what it has sown.