By doing partnership big pharma's can get involved in the trial...

By doing partnership big pharma's can get involved in the trial stage & see for themselves how the drug works. They can have more say in dosage quantity & timing. They can also initiate specific trials those are more important to them.
Big companies don’t mind paying extra as for them it’s more important to be sure what they buy works first. Look at Apple they bought out over 20 companies in the last 18 months or so and paid a premium but wanted to make sure the tech worked first before putting in a bid. Same scenario will play out here.