The New York Yankees never actually asked Donald Trump to throw out the first pitch at their August 15th game against the Boston Red Sox according to the New York Times. Trump was apparently jealous of the attention Dr. Anthony Fauci got when he threw out his ill-fated first pitch to start the MLB season in Washington earlier this month, so he penciled himself into the Yankees' lineup for August 15th.
It's not as if Trump couldn't have thrown out the pitch because he apparently had a standing offer from Yankees president Randy Levine to do so, but the announcement still took everyone by surprise. As they were taken by surprise when he said he was unavailable to throw out the first pitch for the game a few days later.
So why did Trump pick the August 15th game? Probably because it was a Yankees - Red Sox game broadcast on FOX, but that date and not August 1st under the exact same circumstances? I guess wait and see where he plays golf those weekends and we'll be able to figure it out.