If
4e was doing poorly in sales, I have to think that the *last* thing on
WotC's mind would be spending any resources on increasing third party support. Further, considering how long it takes companies to move from data to action, I don't think it's too likely that they would move on poor sales data (remember,
4e only came out a couple of months ago) to changing the
GSL in this time frame.
I think it's far more likely that the
GSL was so long delayed because of competing pressures between legal, business and those with a closer relationship with the third parties in question. The version was released with agony like pulling teeth with far more restrictions than many would like. In the meantime, those in the company who wanted a different
GSL writing kept fighting for another version. The
GSL produced a general lack of interest in using the license (and a subsequent closer examination by some of the options available to the third parties if they did not accept the
GSL). This was then used to convince the powers that be that a
GSL that produced no interest was pretty pointless and needed to be revised.