poetry: --sync removes pkg-resources, leading to pillow error

• Poetry version: 1.2.1
• Python version: 3.8.10
• OS version and name: Ubuntu 20.04.3 LTS
• pyproject.toml:

[tool.poetry]
name = "test1"
version = "0.1.0"
description = ""
authors = ["Claudia"]

[tool.poetry.dependencies]
python = "~3.8"

[tool.poetry.dev-dependencies]

[build-system]
requires = ["poetry-core>=1.0.0"]
build-backend = "poetry.core.masonry.api"

Issue

When running poetry install --sync, poetry removes anything pre-installed (as it should), unfortunately this includes pkg-resources (see #2673 for a discussion), which is pre-installed. Removing this package leads to an error when trying to then poetry add pillow, as discussed in #5104.

I also tried this with Poetry 1.2.0b2, mentioned in #5104 - same problem.