No license, GPL or otherwise, can prevent the situation you describe. If the project is licensed under the GPL, and the company decides it's not turning sufficient profit while remaining open source, then they'll simply stop working on the project and the outcome is the same.
Any open source project can only thrive if the community puts the effort in. Choosing GPL does not prevent or even lessen the risk that a company will decide to stop putting forth the effort.
>> Choosing GPL does not prevent or even lessen the risk that a company will decide to stop putting forth the effort.
True, but it prevents the scenario where a company makes a well supported closed version leaving the rest of the community at a disadvantage in terms of development resources.
Suppose a project has 10 commercial developers and 2 hobbyist developers. The company decided to close source and the open source version is forked. The commercial version now has 10 developers while the open version has 2. That's going to be hard to compete. Now if the same project was GPL with no CLA and the company decided they don't want to contribute to open source, they'll cease contributions but there is no closed fork. The project still exists with 2 people working on it but no competing project. Users will stick with the open version as long as it is viable.
After all the fiascos of companies changing the license on stuff, I’m a fan of what Linux. No copyright assignment and lots of contributors so relicensing is nearly impossible.
Any open source project can only thrive if the community puts the effort in. Choosing GPL does not prevent or even lessen the risk that a company will decide to stop putting forth the effort.