If you are using a git-backed project and have noticed that packages in the requirements.txt file are not being installed, you've come across a bug that affects some Domino versions 4.4+. This should be fixed in Domino version 5.2+.
There are two options to resolve the issue:
1) Move the requirements.txt file to the Artifacts folder of your Domino project
2) Run pip install -r requirements.txt in the pre-setup script (within the project's environment)
If neither of those work for you please reach out to support and we'll do our best to help!