Because the law says it does.
There is a specific rule - IRC 402A(c)(4)(E) - that says amounts transferred from a pre-tax account to a Roth account will be "treated as a distribution" which is why you can do this. There is no rule that says you can net your RMD against your planned contributions for the year and avoid taking a distribution if you contribute less.
"Seems to" is not the same thing as "is." The main thing you're missing is that qualified plans have to have their assets in a trust, under the control of a trustee. Under your method, the trust never has control of the amount, so it can't be considered to be plan assets, so it can't be used to satisfy the RMD requirements.
Your chart also seems to be saying that the $10,000 will simply remain in the business account. The RMD doesn't get paid to the business, it gets paid to the participant. The business would have to pay it out to the participant in that case, and there might be questions why a payment directly from the business to an employee isn't being treated as wages.
If the goal is just to avoid making a payment out of the main plan account, what you might be able to do is to open a checking account in the name of the plan. Then deposit the $15,000 to that account, transfer $5,000 of it to the main plan account, and pay out the remaining $10,000 to the owner. That seems unnecessarily complicated to me, but maybe it will accomplish your aims.