For most companies, the lawyers don't understand the LGPL or software at all, so they don't understand that the LGPL lets the company distribute binaries with Qt libraries included without any source release requirements. They just need to include a notice that Qt is used and where to get the LGPL parts source.
They just like being able to pay money and "own" the IP.
The only time a company actually needs the commercial option is when they distribute in house modified Qt libraries, because those would be derivative works. And I would really want to know why the hell any company thinks its worth it to buy a commercial license so they don't have to release their modifications to Qt itself. That is just ridiculous.
As well, the licensing cost of the enterprise license is $200 a month, that's so cheap compared to a developers salary there isn't a lot of reason not to get it.
Then you can do a static link and make your application a lot smaller (depending on what parts of Qt you actually use) and make installation simpler.
I really like Qt, but I don't use it for a lot of my simple commandline apps because it would turn what could be a <500KB single .exe into a .exe that requires a few MB of DLLs.
I could see some reasons why a company would want to statically link Qt libraries into a larger binary. For that they'll need the commercial license.
I'm just surprised that's a good business model too. I don't quite understand it. Maybe there's something I could read instead of asking the lazyweb?