We can't be sure he had no info on that. All we know is that we, the player, were not told about all the info that Hojo did have. He certainly knew more about Weapon than anyone else in Rufus' entourage:
When Hojo comes with Rufus to the Northern Crater, he could just as easily be Rufus' prisoner as Rufus' employee.
I'm not talking about at the Northern Crater. We're talking about afterwards. Tifa was out for a week. During that week Rufus had all the time in the world to extract whatever info Hojo was willing to divulge. We don't see Hojo until Rufus dies but we are far from told that he escaped imprisonment.
But Rufus would not know that Hojo did not know this. All Rufus knows is that Hoo masterminded the program that created both Sephiroth and Cloud. Like Tres said, Hojo knows more than anyone else. That alone makes him uniquely valuable, even if he doesn't know - or won't tell - everything.
Rufus knew a LOT more then that about Hojo. He knew for example that Hojo knew all along that Sephiroth wasn't an Ancient when Rufus was trekking all over the world following Sephiroth's movements in the hopes it would lead him to the Promised Land. He knew that Hojo had brought Jenova to the Shinra Tower in the hopes that it would lead the Sephiroth clones there. He knew by this time that Hojo knew about Cloud's condition, and the fact that Sephiroth was leading him long before anyone else. He also knew Hojo didn't bother to tell him about the Weapon until their board of Directors was standing right next to it's eye.
These are all things that greatly contributed to the death of Shinra personel, Rufus' father, the endangering of the entire Planet and the repeated endangering of Rufus' own life.
Rufus has not seen much 'enthusiasm for putting an end to Sephiroth' from AVALANCHE. What he has seen is their failure on numerous occasions to conclusively defeat Sephiroth, including their inability to prevent him from killing someone who was uniquely valuable to ShinRa, while on at least three occasions he has either witnessed Cloud being controlled by Sephiroth or would have told about it by Reeve.
AVALANCHE may have proved themselves no less competent than the Turks and the Shinra military, but they have not, at this juncture in the game, proved that they are able - or even willing - to defeat Sephiroth.
Now we are being very selective about what Rufus does and doesn't know. Cait Sith worked as a spy for Shinra early on, but I didn't get the impression they knew Reeve was his controller. Otherwise Scarlet would have had him killed for his open treason by then. Rufus WOULD have some idea that AVALANCHE vanquished the Sephiroth on the boat they were on while he and Heidegger hid in a corner, with all their guards dead. And that at some point AVALANCHE reobtained the Black Materia from Sephiroth before Cloud did his thing again. This is after Sephiroth slaughered the upper level of the Shinra Tower to the man and then vanished, walked through Junon's defenses practically unopposed and the only encounter the Turks had with them lost them their leader.
Rufus had every reason to believe he could use their help at this point, no matter how bleak a picture you believe the malicious Reeve drew of their capacity.
And in fact when they lose Cloud AVALANCHE also lose any interest in tackling Sephiroth; IIRC they spend their time under Cid's leadership flying around in the Highwind trying to thwart ShinRa's attempts to do something about Meteor. As far as Rufus is concerned, Cloud is dead, gone, and AVALANCHE has neither the interest nor the ability to tackle the threat facing the planet.
This was after he tried to kill them, to Rufus' credit after they get away, he doesn't pay much mind to giving them pursuit, he had bigger fish to fry.