I think one of the declines in usage comes from the explosion in open source libraries (as opposed to programs).<p>If you're releasing a library as open source, the GPL all but guarantees you'll see no use in commercial software. This means your audience is limited, and if there are 'competing' libraries that have more permissive licenses, they'll likely become more popular. Less usage and audience means less contributors, testing, and visibility, and that's really one of the biggest benefits of open sourcing in the first place.<p>There's also a compounding effect here, as anyone who is also releasing a library has to make the same decision about their own license, and using code that is GPL means they have to be GPL as well.