Well there were 2 different license problems. The original one around the first KDE releases, with the uncertainty whether the Qt license was GPL compatible. This legal uncertainty at least contributed to KDE not becoming the undisputed leading free mainstream desktop, and would have later caused problems with commercial viability of the platform. Then when Trolltech went dual-license, the platform was legally in the clear, but had a non-ideal developer proposition. It's not an accident that no distro that targeted the commercial desktop went with KDE, despite KDE's obvious technical advantages. Depending on your POV that can be argued to be a good thing, but commercially it wasn't.