If the SSA sold the revenue stream from contribution to the US Department of the Treasury, that might have been enough to make it a tax.
Re: endorsements, I'd have to chalk it up to the attorneys-at-bar. I recall how adamant a bank was back in the mid 90s about absolutely NOT making any changes to the format of checks --that is, if they printed them. They offer free check printing because its not likely that you'll go print your own. There are at least two ways to make something payable to order:
orPay to the order of...
The attorneys probably suggested the former over the latter. With the latter (the 2nd one) there shouldnt be any need to do anything but "show ID". There'd be no need to endorse the 2nd at the drawer's bank, of course, the payee wanted to give an order. Of course, the same "Pay .. to the order of" verbiage pervades Quickbooks and perhaps almost every popular check printing or accounting software package on the planet. You're just not "supposed" to know there is any alternative because the conditioning and misleading called "education" is just "supposed" to work.Pay to ......................... or order
If you cross the Pacific to, say, New Zealand you dont see that kind of wording on checks. Instead you see something like..
Pay ...
The sum of...