Установка докера с помощью snap и apt-get

Я пытаюсь установить докер на свой Ubuntu 20.04. Попытка установить докер с помощью apt-get и snap :

sudo apt-get install docker

Вывод:

Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following additional packages will be installed:
  wmdocker
The following NEW packages will be installed:
  docker wmdocker
0 upgraded, 2 newly installed, 0 to remove and 6 not upgraded.
Need to get 0 B/14.3 kB of archives.
After this operation, 58.4 kB of additional disk space will be used.
Do you want to continue? [Y/n] y
Selecting previously unselected package wmdocker.
(Reading database ... 193518 files and directories currently installed.)
Preparing to unpack .../wmdocker_1.5-2_amd64.deb ...
Unpacking wmdocker (1.5-2) ...
Selecting previously unselected package docker.
Preparing to unpack .../archives/docker_1.5-2_all.deb ...
Unpacking docker (1.5-2) ...
Setting up wmdocker (1.5-2) ...
Setting up docker (1.5-2) ...
Processing triggers for man-db (2.9.1-1) ...

Если я запустил команду docker, я получаю сообщение об ошибке:

a@ubuntu:~$ docker

Command 'docker' not found, but can be installed with:

sudo snap install docker     # version 19.03.11, or
sudo apt  install docker.io  # version 19.03.8-0ubuntu1.20.04.1

See 'snap info docker' for additional versions.

Почему система не может найти команду docker ?

Затем я привязал оснастку:

sudo snap install docker 

И команда docker работает нормально.

Почему я могу установить докер с помощью оснастки, а не с помощью apt-get?