Filled all RAM slots and getting slow memory

I have [URL=https://www.asrock.com/mb/AMD/TRX40%20Creator/#Specification]ASRock TRX40 Creator[/URL] motherboard which accepts 8 modules of DDR4, the MB's documentation says that in order to enable 4 channels of RAM I have to put more than 4 modules, so, I wanted to have fast RAM and purchased [URL=https://www.newegg.com/g-skill-64gb-288-pin-ddr4-sdram/p/N82E16820232281?Item=N82E16820232281]G.SKILL Ripjaws V Series 64GB (8 x 8GB) 288-Pin DDR4 SDRAM DDR4 3200 (PC4 25600) Desktop Memory Model F4-3200C14Q2-64GVK[/URL].

Once I put all 8 modules I noticed a very low frequency - 2133MHz. Can you please tell me why this is happening and how to fix it? The MB's manual doesn't say anything about any dependency between number of modules and frequency.