If you’re working on your own you may not need dagger.
If you’re working on a team often your shell scripts, python programs, and makes files are not always portable between local and CI, but even worse between your local machine and your colleagues local machine. This is where dagger shines because it lets you do all that stuff in a fully portable way.
I need an example to illustrate that, because I had to read this thread to even understand what I was reading/looking at.
A lot of projects and teams have been successfully using all tools mentioned in both CI and local dev envs. Portability and reusability of this “glue” stuff is a nice indicator of engineering maturity and culture within those projects and teams.
Low pro teams and individuals will happily abuse any new tool.
Mature teams stick to local-first CI - i.e. be able to run pipeline locally - and then translate to whatever is being used in their build and test infrastructure.