When I first started writing children's stories in 1979, I got ... a lot of rejection slips. One thing I learned from them is that there is no one reason for the rejection.
The writing
The timing
The subject matter
They're booked through the year
On and on. But they'll rarely explain any of this so best not to take it personal, other than as a motivation to keep trying and writing.
"No doesn't mean you are not good enough"
Perfect takeaway! 😉👏