Why Use Aluminum for a TT Platter?

The idea of "big" or extremely heavy platters is mostly for use with belt drive tables which I believe, in terms of speed accuracy, are clearly inferior to properly implemented direct drive tables.

And yes, when it comes to belt drive, it is about inertia. "An object in motion remains in motion unless acted upon by an outside force".

Just look at the platter of the relatively inexpensive ($2k) Nottingham Spacedeck. It's a minimalist design table, and I bet that the platter alone costs at least half, probably more. I have no idea what it is made of but the thing is quite heavy. As I understand, that's what mostly makes Nottinghams sound the way they do - the platter.
Cooper with lead and steel in a sandwich style sounds good to me. And a beer please.

Viridian thanks for the trademark education but Michell platters are Carbon infused acrylic that DO contain Vynil.
Cheers

"Belt drives...in terms of speed accuracy, are clearly inferior to properly implemented direct drive tables."

Humm, proof, evidence to back this up?

Nothing cogs like a DD. The mass of the platter has nothing to do with flywheel inertia.