Installing 'tkinter' on Linux for Python3

I find it confusing that the python module 'tkinter', the interface module for the tk scripting language, is only installable via the Linux platform package manager. On Ubuntu I used:

sudo apt-get install python3-tk

and then in python3 I can import tkinter:

Python 3.9.5 (default, May 11 2021, 08:20:37) 
[GCC 10.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import tkinter
>>> quit()

Using pip3 directly to install tkinter doesn't work, nor does pip3 install tk, which installs an unrelated module.

For python2 remove the '3' from the above commands.