Microsoft somehow sees a future where LLMs have access to everything in your screen. In that dystopia, adding "confidential" tags or prompt instructions to ignore some types of content is never going to be enough. If you don't want LLMs to exfiltrate content then they cannot have access to it, period.
Microsoft wants access to everything in your screen (as well as the contents of your personal files) and feeding that to an LLM just makes it easier for them to profit from that data