Well, the vast majority of people aren’t running operating systems that require the use of docker or even really support it. So now you’re looking at 5% of users who would need to install docker.

Of those users 90% are running Debian. So you insert apt install docker into your script. The remaining .4% are using red hat. So you insert yum install docker into your bash script.

Then you add a line to start your image, now put the bash script on your website, voila, single file program that works anywhere.