[_heimdall]

Wouldn't a compliance investigation effectively just be the evidence collection phase before a charge is filed, assuming the evidence supports it?

I wouldn't expect them to write the law and immediately charge Google, for example, based only on public knowledge and no compiled evidence.

[Vespasian]

Yes. It's basically the reply to their (in my layman's view) offensive non-compliance.

They had plenty time to figure it out and now they may reap what they sowed. Not everybody tried to play games e.g. notice how Microsoft is not a subject of this specific investigation.

This is probably also a final warning shot. I'm certain that if they "suddenly" and "on their own" find ways to "correct" their software and business practices this investigation can be closed without charges brought forward.