The ugly truth is, that these applications were never developed with any respect for these things and there is a lot that is “wrong” with it

When those applications came to being, all the current environment with containers didnt exist even in theory, leave aside in practice.

Those applications were created for fulfilling the needs of certain audiences (in WP’s case, it happens to be ~35% of entire internet), and they were designed and they evolved for that purpose with maximum flexibility. And be accessible in every way — from usage to cost. That was their purpose, and they still fulfill it splendidly. Taking WP as an example, it can run from $5/month shared hosting to load balanced clusters.

Containerized environment is the newcomer to the scene. And it must evolve itself to accommodate existing usage cases. Expecting entire IT space to bend themselves at the cost of properly fulfilling actual usage needs of users would be unproductive.