I've had arguments with people about this for 20 years now and the most compelling case I heard involved the price of storage vs the price of RAM in the mid to late 1990s, and that this 2x represented an optimal use of money in designing a system at that point in time.

Also I still put my swap partition at the end of the drive out of habit because you used to want to do that for performance reasons when it was stored on a spinning magnet.