MSI representatives revealed that offering backwards compatibility for the Ryzen 3000 series processors on AMD 300-series and 400-series based motherboards took quite a bit of work. The issue is that many of those motherboards use a 16MB SPI flash EEPROM chip and that wasn't enough for MSI to implement the AGESA ComboAM4 188.8.131.52a microcode.
Therefore, MSI had to kick out quite a bit of features and sacrifice SATA RAID on many of its motherboards:
The company had to make several changes to its UEFI BIOS package that's currently being circulated as a "beta," to accommodate support for 3rd generation Ryzen processors along with AGESA ComboAM4 184.108.40.206a. First, it had to kick out support for A-series and Athlon processors based on the 28 nm "Bristol Ridge" silicon. Second, it had to [and this is a big one], kick the RAID module, breaking SATA RAID on many of its motherboards. Third, it had to replace its feature-rich Click BIOS 5 setup program with a barebones "GSE Lite" Click BIOS program, which lacks many of the features of the original program, and comes with a dull, low-resolution UI. This program still includes some essential MSI-exclusive features such as A-XMP (which translates Intel XMP profiles to AMD-compatible settings), Smart Fan, and M-Flash.
Many other motherboard makers also used 16MB chips for their 300-series and 400-series chips so caution is advised when you upgrade the BIOS to the latest version. If you're not planning to use a new Zen 2-based chip on these motherboards, it may be wise to stick with your current BIOS version as an update may result in a loss of features. MSI specifically warns not to update to these BIOS versions if you've already set RAID for your system.
The new X570-based motherboards use a 32MB EEPROM chip so this shouldn't be an issue in the future.