Why shouldn't languages have a logo? It's not just a commercial/corporate thing, a clear visual identity can help tie any project together. It makes it easier for users to identify material and organisations related to the project and its ecosystem.

As an example, the Python, PHP and Java logos are very distinctive in their own ways, and when you're sifting through YouTube tutorials as a beginner, seeing the logos pop up in thumbnails can help you spot material that's relevant to your learning.