With respect to Eclipse itself, it has dramatically improved over the last few years, since the Foundation started making a release every 3 months. IMHO, for Theia to become really meaningful the server-side part needs to be improved: currently Theia reuses Eclipse JDT and other plug-ins on the back-end, which is fine for a desktop app, but less convenient for a client/server IDE as you will need a separate server-side container running the Eclipse plug-ins for every active user running the Web-based Theia GUI. They are now focusing on the user interface and plug-in architecture of Theia (which is already capable of running VSCode extension). It is meant to be usable for building cloud-based IDEs, and you can test a distribution on your workstation, but being it a client/server architecture, you currently have to run a docker container locally to test Theia (or at least this was the case in Q3 2023).
My understanding is that Theia is currently more of a platform than a complete IDE. It's not peculiar to Eclipse Foundation, many open source vendors require contributors to sign a CLA That's a legal requirement to protect the Foundation from contributions that may copy/paste proprietary code and to ensure that you will not in the future change your mind and make claims for your contributions. You don't have to sign the CLA (contributor license agreement) if you want to report a bug, but you have if you want to contribute code, even a small patch for a bug you found.
Hi, I am an Eclipse Foundation committer, but I am not committing to the IDE itself.