Takuma Hisa Discusses One Aspect of This Here
Tokimune Takeda extends the connection back further in this interview.
So my question is: Why is it that Daito Ryu seems to want to "Hang its hat" on Ono Ha Itto Ryu? Why not Jikishinkage Ryu? Or perhaps "Takeda ha Shinkage Ryu" or some other moniker unique to Takeda Sokaku? Not that I have anything against Ono Ha Itto Ryu. I'm just asking, "Why them to the exclusion of others? And, "Is there proof that this exclusive wedding of Ono Ha Itto Ryu with Daito Ryu came directly from Takeda Sokaku?"
I think the more specific answer to your question would be: because Ono Ha Itto Ryu was the sword art that Tokimune's students were encouraged to study.