In the loosest sense this USDC is in a vault backing DAI. You are asking to swap this for MKR which has a predictable price movement (down if for any reason if the protocol is losing money). This has terrible implications.
I have long supported the idea of putting a good chunk of this USDC into a 100% liquid contract (USDC-DAI on Uniswap for example) to earn return. We could have dropped it into compound or AAVE but none of these have 100% liquidity. The biggest issue here is we don’t want to fully depreciate this facility because we want USDC here to buy if the markets want to sell DAI for USDC. USDC in the PSM is the DAI downside PEG protection, vaults next, SF and DSR raises 3rd and 4th.
If Maker were to convert all of this USDC into a bond we would lose our downside PEG protection.