Typically the ability of savants to remember things isn't markedly better than
contestants in the memory championships. For example, the winner of the one-hour playing card contest this year memorized 1404 playing cards (suits and numbers), before making an error on the 1405th card - and that isn't all that unusual his closest competitors were 1352 and 1305.
None of these people are savants either - they're just regular people who practice memorization competitively.
The speed card winner memorized a pack of 52 cards correctly in just 21 seconds - or
4/10ths of a second per card (and he only barely beat out second and third place by like less than a second?) - they basically just flip through the entire deck staring at the corner and then recite it back on the spot. These are not oddities of nature - human beings have an incredible capacity for practiced memorization, but it requires
practice. You could train to become almost as good as any of them in a year of daily exercises.
It's not anything new either - the ancient greeks as early as 400 BCE (and probably much earlier) used the
Method of Loci technique to competitively memorize as well - Cicero considered it an essential skill of any great orator to commit the speech to memory so they wouldn't need notes/teleprompters and could focus entirely on their delivery.
We use 100% of our brains, most people just aren't very practiced in memorization is all.