The reason for this is that mining directly to your own Bitcoin Core node is no longer supported due to certain technical limitations.
There are right about a dozen wrong statements in your comment, mining to your own node is still possible, using the word supported is rather wrong because that brings up a question; "supported by who"?
Mining to ones node will always be possible given how
BTC works, it's just a question of feasibility and nothing more.
Since mining is highly competitive, the probability of an individual miner finding a block is quite low.
Every block found on the network is found by a single small miner, many people mined individually and managed to find blocks, some did that with USB sticks that don't mine faster than a few gigahashes per second, besides, we don't know OP' hashrate, he could be mining with 10EH worth of hashrate, so his chances of finding blocks mining to his node are a lot larger than the changes of couple mining pools combined.
The only drawback of mining to your own node would be the reliability aspect, mining isn't just about getting lucky and hitting a block, you need to stay constantly synced with other nodes, and you need to have a very fast connection to other nodes (especially the mining ones), block downloading, processing, and prorogation are very sensitive and there is zero room for error, it's plain stupid to risk losing blocks by mining to a node that runs on an old laptop sitting in the garage hooked up to your not so reliable 10mbps ADSL.