RHI (Robert Half) collecting reams of personal data to what ends?

I received a call from an RHI recruiter recently.
I was asked to come in for an interview to discuss as yet undisclosed positions.
When I got to the office the 1st thing they wanted was an a signed blanket agreement for them to be able to do background checks at will and indemnifying them from any damages, a signed W4,
and signed I9 and a signed employment contract,and some stuff about HIPPA.
All this before even have a single word about potential jobs.

Now I've worked for many agencies.
In all cases I was asked to sign a huge pile of documents just prior to starting on
a contract. Each time there was something about non-compete and not stealing their clients etc. I can understand that, and I signed. No problem.

But RHI even goes as far as to get your Social security number, and
all your personal info before any job is even spoken about.

It appears they are trying to establish that you are "employed" by them though you have yet to ever receive a paycheck from them.

I objected to giving them a copy of my Birth cert, and signing an employment contract before the interview when I already am employed. Not to
The contract reads that "This agreement is entered into on XX date, By John Doe and RHI.
Consultant agrees to provide on as needed basis as are required from "time to time".
It appears they are essentially saying you are ALREADY employed by them.

Then just a little ways down the page, it says "Consultant shall NOT
during Consultants 'period of employment' (which I'm guessing they mean the date you came in for the interview) perform ANY services for ANY other company or individual similar to the services being provided hereunder without obtaining RHT's written consent,"

This is exactly the scenario that I experienced with Robert Half. Unspecified probably non-existent jobs, and requests for a gazillion documents and personal information just to meet with a recruiter. I did not proceed forward.