For Github Actions, the product launch has been a major success and has become a new monetizable product. Anecdotally, I've heard of some companies moving their Jenkins/Circle CI/Travis CI workflows over to it, better proof is the sheer number of Github Actions that are now easy to install. This also allows Github to compete directly with Bitbucket and Bitbucket pipelines.
If your question is about who is asking for Github Codespaces, I'm not totally sure. Personally, for small changes it would be nice to be able to edit directly in Github but I certainly wouldn't pay for it. I imagine that core why behind this product release (besides the fact that most of this functionality was already pre-built and easy to reuse) is that it improves the user experience for anyone working from their chromeOS device, tablet and phone improving brand loyalty and capturing new users, especially students who may only have chromeOS devices.
As an OSS developer, Github actions make a lot of sense and is very welcome since it's very easy to setup (now! it was impossible in the beginning) and if you use bash scripts/npm scripts AND a tiny bit of workflow code then they are very agnostic as well.
I am unsure about this Github Codespaces though, I'll be testing it but I am fairly skeptical about invest a lot in Github-specific tooling beyond what is needed by a typical repo. It seems like Github has been trying to "extend" git into a proprietary phase for a while, and now with Microsoft backing it I'll wait to see if it's still the same old concept of locking you in deep and then do as they please. Not sure, it does look like they are going nice for now, but I personally prefer to wait.
This Codespaces doesn't solve a specific need I could point out like Actions did before, but maybe I'm just not their target.
I can imagine this being very useful in educational settings. Instead of students and teachers spending time on getting everyone's lab environments set up they just fork the course repository and tada it's there and it works.
For private repos, Codespaces will help on-boarding new team members or employees who don't have to waste time setting up a dev environment to contribute back.
If your question is about who is asking for Github Codespaces, I'm not totally sure. Personally, for small changes it would be nice to be able to edit directly in Github but I certainly wouldn't pay for it. I imagine that core why behind this product release (besides the fact that most of this functionality was already pre-built and easy to reuse) is that it improves the user experience for anyone working from their chromeOS device, tablet and phone improving brand loyalty and capturing new users, especially students who may only have chromeOS devices.