Officially it was for "near-peer threats," so Russia/China/Iran. The program started in 2017, back when Russia was showing off Ratnik (which never existed) and personal armor that could stop .50 BMG dead in its tracks (which also didn't exist). The US was preparing Ukraine for an invasion that they knew was coming, which is why they originally wanted the winner chosen by October of last year, but further testing was required and it got delayed another 6 months.
The PLA didn't even mention the need for body armor until a year later in their 2018 roadmap, and didn't order any until two years after that. I find it kind of strange that the Chinese waited so long, because Americans had been buying cheap Chinese ceramic plates on Wish.com for years prior (though only about 5% were as strong as advertised, most were just hard plastic or incredibly shitty quality, a few were good).