Earlier quoted context omitted.
Like other folks have said, anytime you see a CLA, you see the true intentions of the project. A project that will always be FOSS won't have a need for a CLA.
This is not necessarily true. Sometimes it's needed to pivot to a better/different open source license without going through the pain of contacting every contributor ever. I have seen that pain in some projects that want to go from LGPL to MIT or something. For many contributors, they're ok giving full ownership of their contributions to a project owner on the owner's terms. Some contributors may not be ok with that…
Someone who is has a strong preference for copyleft licences may not want to contribute to a project with a permissive license.
The intent may not be for the project owners to use the code in proprietary software, but it would be to allow someone to do so.