Private class members

Problem/Motivation

In https://www.drupal.org/project/entity_usage/issues/3468898 ✨ Modernize services: Add autowiring aliases, use autoconfigure, etc Fixed all the class properties were changed to private. What was the actual reason / benefit of it? I am asking because I have a project where the EntityUsage service is overwritten, and I am using the connection class property from the base class. Now I have a fatal error because of that.