As a way of showing that PLAN can get a 20-frigate class before US will launch the first one from their own 20-ship order.
Jokes aside, we don't know for sure.
Probably a combination of need for more multi-role combatants with delays in 054b development. The international climate is deteriorating, fast.
Furthermore, even if US frigate-printing capability doesn't show much promise yet, JMSDF frigate line actually works.
I am not sure if the idea of not having VLS on your frigates work, nor having an S-band search radar.