They started with their own license, which was considered to be incompatible with GPL. Only later it was changed to GPL.<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Qt_(software)#Licensing" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Qt_(software)#Licensing</a>