python -m pip install pygame実行時にエラー

$ python -m pip install pygame
Collecting pygame
  Cache entry deserialization failed, entry ignored
  Cache entry deserialization failed, entry ignored
  Downloading https://files.pythonhosted.org/packages/bc/0c/d164411381bada8feae57359aa9296defbed3035f4b55bef6a271cb0573c/pygame-2.0.0.tar.gz (5.5MB)
    100% |████████████████████████████████| 5.5MB 72kB/s 
    Complete output from command python setup.py egg_info:
    
    
    WARNING, No "Setup" File Exists, Running "buildconfig/config.py"
    Using UNIX configuration...
    
    sh: 1: sdl2-config: not found
    sh: 1: sdl2-config: not found
    sh: 1: sdl2-config: not found
    
    Hunting dependencies...
    
    ---
    For help with compilation see:
        https://www.pygame.org/wiki/CompileUbuntu
    To contribute to pygame development see:
        https://www.pygame.org/contribute.html
    ---
    
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/tmp/pip-build-yovQQX/pygame/setup.py", line 318, in <module>
        buildconfig.config.main(AUTO_CONFIG)
      File "buildconfig/config.py", line 221, in main
        deps = CFG.main(**kwds)
      File "buildconfig/config_unix.py", line 194, in main
        DependencyProg('SDL', 'SDL_CONFIG', 'sdl2-config', '2.0', ['sdl']),
      File "buildconfig/config_unix.py", line 39, in __init__
        self.ver = config[0].strip()
    IndexError: list index out of range
    
    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-build-yovQQX/pygame/

python -m pip install pygame==1.9.6にすると解決、なぜ、、

$ python -m pip install pygame==1.9.6
Collecting pygame==1.9.6
  Cache entry deserialization failed, entry ignored
  Downloading https://files.pythonhosted.org/packages/0f/9c/78626be04e193c0624842090fe5555b3805c050dfaa81c8094d6441db2be/pygame-1.9.6.tar.gz (3.2MB)
    100% |████████████████████████████████| 3.2MB 139kB/s 
Building wheels for collected packages: pygame
  Running setup.py bdist_wheel for pygame ... done
  Stored in directory: /home/jetson/.cache/pip/wheels/79/87/65/8b9b165b8f56109ce465665aa44c994f103d428b815ceedc8a
Successfully built pygame
Installing collected packages: pygame
Successfully installed pygame-1.9.6