If The Qt Company discontinued the FOSS version of Qt, the Qt framework would become available under the BSD license, and there would no longer be a contributor licence agreement allowing a company to sell the work of another company.
> in addition to all the third-party contributions, which are a small, but not insignificant portion of the Qt code.
In the last years more than 50% were open source contributions. At Nokia times they were only 10 to 20%.