For sure, it's arm twisting and/or individual moles, I doubt Apple is brimming with patriotism. As far as I remember participation in the OG PRISM wasn't really optional, the only "perks" were immunity from civil liability. I assume that any of the "lucky" individuals that have to interface with the NSA are well compensated. They also know they are on a veeery short leash.
The other option is good ye old agent cultivation, there must be a degenerate gambler high up in Apple that the MSS or FSB can exploit.