https://mdshock.com/2019/03/18/sega-and-sony-new-insight-int...
That article also gives insight into why Kutaragi/Sony wanted to partner with Nintendo.
A quote by Kutaragi:
“I wanted to start up a business that would become a new major income source for the company in the future… [Sony executives] thought it would take too long to start a new business from scratch with venture capital. So the only way to initiate change was from the outside. We could join forces with the best-performing company in the field. We would sell them our technology, establish a track record, and use that as the springboard to future success. That was my reasoning.”
Also, from historian Reiji Asakura:
“Nintendo was concerned that its business would eventually be taken over by Sony if Sony continued to drive product development. Although Nintendo was dominant in the game-machine market, the company was fully aware that Sony had a superior research-and-development operation and thus had the potential to outstrip its competitors in the area of technological advancement.”
References are in the linked article.