Only the miner (or mining pool) that created that block will know for certain exactly why that was done in that exact transaction, but here are a few common reasons I can think of that miners (or pools) might do it.
1. Perhaps it is a pool that immediately awards all pool participants with their earnings in the block as it is mined. So, if there are 100 people all participating in a pool, the pool might build blocks with the block reward already split up to the participant's addresses.
2. Perhaps a solo miner wants to split up their earnings between some hot wallets and some cold wallets. It is safer to send the value directly to the cold wallets as the value is earned, rather than sending it to a hot wallet and then creating a separate transaction to forward that value to a cold wallet later.
3. Perhaps a solo miner is attempting to increase their level of privacy by having multiple wallets that are each used for different purposes.