The most probable reason is down to that they didn't need to as most of the figures had been available on their domestic cards for some time. Despite great overseas sucess, General Mills were consolidating production and logistics under one banner, rather than the individual domestic distributors.
New figures were released in the new style packaging, but to back fill an exisiting range was possibly only done to clear and re-distribute overstock.
You need to remember that this was the principle behind POTF too, but it never got that far, Tri-logo had the advantage of a possible wider distribution.
As a line, Trilogo is actually caters the great majority at a time when it was confirmed there would be no new movies. There was very likely that artwork existed for those figures, but the print costs versus the stock left probably mean't that it wasn't cost effective and easier to filter out those remaining under other methods.