Most of it is a personal preference. I'd rather pull the full repo of my dependencies in rather than "deal" with submodules. Submodules add some extra necessary

Most of it is a personal preference. I'd rather pull the full repo of my dependencies in rather than "deal" with submodules. Submodules add some extra necessary workflow steps that others contributing to your repo might not be expecting. Subtree simplifies a lot of that. As well, I think it helps to solidify the "reproducible build" concept by taking submodules 1 step further.