Stating that nothing has happened is not accurate. Three years ago we started building a comprehensive toolset specifically for collection development. That effort resulted in the release of Ansible Development Tools (ADT).
To highlight just a few pieces, we introduced ansible-creator and modernized Molecule to more natively support collections. There is a lot more in ADT, including dedicated pytest-ansible and tox-ansible plugins. The only outstanding feature we might be missing is “sanity” (a problematic term we need to discard) testing. Honestly, for me and some others, it is hard to gauge how much of that type of testing collections actually need versus ansible-core.
ADT is not perfect and we always welcome feedback. However, the tools are out there and actively maintained, so asserting that “nothing happened” is not accurate.