My biggest issue is this: you discover an interesting open source project in a repository, but it is so tightly coupled to its container setup that it is difficult to grasp its inner workings or its core.
I found a cool project buried in various Composer files and containers, only to discover in the end that it could be summarised as two Python scripts.
As an option, Docker is fine. But if the project is so tightly coupled to Docker, it becomes an unnecessary dependency.