Even if you look at your purchase history now they have intentionally destroyed that too. What size shoe did you buy 3 years ago? Too bad we are not telling you!
The purchase/shipped/etc email was the lifeline to tracking your Amazon spending and exactly what you bought. Now that is impossible. It's similar to a business refusing to give you a proper receipt and should be likely illegal.
What 3rd party companies I let hoover up my Amazon purchase emails is none of their business.
Not really having this issue looking through the last 10 years on my account? 1-2 dozen pairs, all have the size info available. Invoice histories seems proper enough - they have the product titles, costs, and seller info but not the entire descriptions.