Not speaking for SEGA (we don't have the rights to Shenmue anymore anyhow), but chances are very, very high that Sony is feeling out the commitment of the fanbase before sinking the tens of millions it will cost to develop.
Yes, Shenmue 2 cost north of $70 million. IIRC, it barely broke even in sales. It was disastrous for SEGA.
Shenmue is a cult favorite, a critical success but not a commercial one. They did this Kickstarter to see if the fanbase was big enough to warrant production. (That said, I wonder how many fans of Shenmue who would buy it aren't just participating in the Kickstarter...)