Erro tkinter ao tentar importar matplotlib.pyplot no Arch Linux

Estou usando Arch Linux com Gnome. Eu usei o pip para instalar o matplotlib no meu diretório inicial:

pip install --user matplotlib

Isso pareceu funcionar e, quando uso o Python, consigo import matplotlib. No entanto, se eu tentar importar matplotlib.pyplot, recebo o erro

>>> import matplotlib.pyplot
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/username/.local/lib/python3.7/site-packages/matplotlib/pyplot.py", line 2374, in <module>
    switch_backend(rcParams["backend"])
  File "/home/username/.local/lib/python3.7/site-packages/matplotlib/pyplot.py", line 207, in switch_backend
    backend_mod = importlib.import_module(backend_name)
  File "/usr/lib/python3.7/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "/home/username/.local/lib/python3.7/site-packages/matplotlib/backends/backend_tkagg.py", line 1, in <module>
    from . import _backend_tk
  File "/home/username/.local/lib/python3.7/site-packages/matplotlib/backends/_backend_tk.py", line 5, in <module>
    import tkinter as Tk
  File "/usr/lib/python3.7/tkinter/__init__.py", line 36, in <module>
    import _tkinter # If this fails your Python may not be configured for Tk
ImportError: libtk8.6.so: cannot open shared object file: No such file or directory

Por que estou recebendo um erro e como posso corrigi-lo?