> Why was the "loose PHP files with no framework" pattern abandoned, but not active record..?

Presumably because people still find active record to be a productive, sane, and scalable way to build web applications, unlike a disorganised collection of files.

> I'm asking what the pros are.

Speed, terseness, simplicity, and personal preference spring to mind.

You're talking as though there is some empirical "best way", but the fact is that every language, framework, tool, and design pattern has pros and cons, and those pros and cons will change depending on the project, and the individual.

Your list of pros and cons may differ to mine, simply because of personal perspective and preference, and that's fine.

Being blunt, I would expect an experienced, senior engineer to understand this.