Often, the contributor license agreement says that you - the contributor - transfer the copyright of your contribution to the project/company.
This is used to get the community contributing to the project while making sure that the project can be turned into a proprietary project at anytime.
The copyright holder can decide about the license. As long as only one entity holds the copyright, this entity is free to change the license. This even works if the project is licensed under a copyleft license like the GNU Public License (GPL). Such projects might look like "open-source". Fine, the source is open at the moment. But it might not be open anymore tomorrow.
You may actually miss out when using an IDE. Driving without training wheels is more fun :)
I've used IDEs (Netbeans, Intellij) in the beginning but then started migrating away. They where just too heavy for me. Also, often IDEs do lots of stuff in the background such that you easily don't understand fully what is going on. Now I settled using the 'helix' text editor. It provides some IDE-like features like integration with language-servers, syntax highlighting, code completion, file navigation, code navigation, symbol search. But there are no dozens of buttons for triggering compilation etc. You do all this on a separate terminal.
Quite handy for such setups are tiling window-managers like i3. They allow you to easily fit the editor and terminals on the screen. This way you also don't need the build-in terminal of an IDE.