But there is a lot of work to be done before you can do the simple apt install. I (gladly) don't know how it is nowadays but before Dockerfiles/Docker creating your own packages according to the various standards was a pita. Most companies needed a 'packaging specialist/release engineer' role as most developers where not up to the task. Solutions like FPM[0] did help somewhat, but it was still hard when dealing with non-homogeneous environments. Containers solved that problem universally for all distributions.

[0] https://github.com/jordansissel/fpm