pex: pex vendoring does not (always) isolate itself from a colliding setuptools install in site-packages

Having issues creating pex files in an image based on databricksruntime/python-virtualenv.

Dockerfile:

FROM databricksruntime/python-virtualenv:latest
RUN apt-get update \
  && apt-get install -y --allow-unauthenticated apt-transport-https ca-certificates curl gnupg2 software-properties-common curl software-properties-common build-essential

# Install & Bootstrap Python 3.7
RUN add-apt-repository ppa:deadsnakes/ppa
RUN apt update
RUN apt install --yes python3.7 python3.7-dev
RUN virtualenv -p python3.7 --system-site-packages /databricks/python3
RUN /databricks/python3/bin/pip3.7 install pex setuptools==45.2.0
ENV PATH="$PATH:/databricks/python3/bin"

Command run in container:

pex --interpreter-constraint='CPython>=3.7' boto3 -o boto3.pex -m boto3

Portion of failure StackTrace:

Traceback (most recent call last):
    File "<string>", line 1, in <module>
    File "/tmp/pip-req-build-kh23prp9/setup.py", line 59, in <module>
      'Programming Language :: Python :: 3.8',
    File "/root/.pex/pip.pex/aef609891d42d65c887d1aeee58c46f6713a7e49/.deps/setuptools/setuptools/__init__.py", line 169, in setup
      return distutils.core.setup(**attrs)
    File "/usr/lib/python3.7/distutils/core.py", line 148, in setup
      dist.run_commands()
    File "/usr/lib/python3.7/distutils/dist.py", line 966, in run_commands
      self.run_command(cmd)
    File "/usr/lib/python3.7/distutils/dist.py", line 985, in run_command
      cmd_obj.run()
    File "/root/.pex/pip.pex/aef609891d42d65c887d1aeee58c46f6713a7e49/.deps/wheel/wheel/bdist_wheel.py", line 228, in run
      self.run_command('install')
    File "/usr/lib/python3.7/distutils/cmd.py", line 313, in run_command
      self.distribution.run_command(command)
    File "/usr/lib/python3.7/distutils/dist.py", line 985, in run_command
      cmd_obj.run()
    File "/root/.pex/pip.pex/aef609891d42d65c887d1aeee58c46f6713a7e49/.deps/setuptools/setuptools/command/install.py", line 65, in run
      return orig.install.run(self)
    File "/usr/lib/python3.7/distutils/command/install.py", line 601, in run
      self.run_command(cmd_name)
    File "/usr/lib/python3.7/distutils/cmd.py", line 313, in run_command
      self.distribution.run_command(command)
    File "/usr/lib/python3.7/distutils/dist.py", line 985, in run_command
      cmd_obj.run()
    File "/root/.pex/pip.pex/aef609891d42d65c887d1aeee58c46f6713a7e49/.deps/setuptools/setuptools/command/install_scripts.py", line 22, in run
      import setuptools.command.easy_install as ei  # vendor:skip
    File "/root/.pex/pip.pex/aef609891d42d65c887d1aeee58c46f6713a7e49/.deps/setuptools/setuptools/command/easy_install.py", line 69, in <module>
      from setuptools.sandbox import run_setup  # vendor:skip
    File "/root/.pex/pip.pex/aef609891d42d65c887d1aeee58c46f6713a7e49/.deps/setuptools/setuptools/sandbox.py", line 24, in <module>
      import pkg_resources.py31compat  # vendor:skip
  ModuleNotFoundError: No module named 'pkg_resources.py31compat'
  ----------------------------------------
  ERROR: Failed building wheel for boto3