[ubuntu(Docker)] pystanがpipにあるにもかかわらずimportできない状況の解消方法

以下のDockerfileで環境を作成したところ,
sys.pathががpystanの置かれている場所を含んでいるにもかかわらず,
pystanがimportできないため,
こちらの解消方法をご教授いただけると幸いです。

.1. Dockerfileの作成

DockerFile
1FROM ubuntu:20.04
2
3RUN apt-get -y update
4RUN apt-get -y install python3
5RUN apt-get -y install jupyter-notebook
6RUN apt-get -y install python3-pip
7RUN pip3 install --upgrade pip
8RUN pip3 install pystan
9RUN pip3 install pandas &&\
10    pip3 install numpy &&\
11    pip3 install matplotlib &&\
12    pip3 install scipy &&\
13    pip3 install scikit-learn  
14RUN update-alternatives --install /usr/bin/python python /usr/bin/python3.8 30
15WORKDIR /workdir

.2. Dockerのbuildを行う

terminal
1$ls
2Dockerfile
3$docker build . -t tmp_teratail

.3. Dockerのrunを行う

terminal
1docker container run -it --rm --net=host  \
2        --mount type=bind,src=`pwd`,dst=/workdir \
3        my_quick \
4        bash

.4. pythonにてimport状況を確認する

terminal
1#python
2>>> import sys, subprocess
3>>> sys.path
4['', '/usr/lib/python38.zip', '/usr/lib/python3.8', '/usr/lib/python3.8/lib-dynload', '/usr/local/lib/python3.8/dist-packages', '/usr/lib/python3/dist-packages']
5>>> subprocess.run("pip3 show pystan",shell=True)
6Name: pystan
7Version: 3.3.0
8Summary: Python interface to Stan, a package for Bayesian inference
9Home-page: https://mc-stan.org
10Author: Allen Riddell
11Author-email: riddella@indiana.edu
12License: ISC
13Location: /usr/local/lib/python3.8/dist-packages
14Requires: aiohttp, clikit, httpstan, numpy, pysimdjson
15Required-by: 
16CompletedProcess(args='pip3 show pystan', returncode=0)
17>>> import pystan
18Traceback (most recent call last):
19  File "<stdin>", line 1, in <module>
20ModuleNotFoundError: No module named 'pystan'