Whilst I get the argument and understand the thinking of why didn't Brock cash in there and then I think It shows that Brock believes he can just show up and beat anyone at anytime and he is just enjoying playing the ''Cash In game'' with Rollins and getting in his head that he is waiting at every corner not knowing when he is gonna strike, like when his entrance music started twice and he didn't show or when he arrived and was heading to the ring but changed his mind
All those things had Rollins on edge
I Don't think anyone but Brock has that aura and Believability to be so confident that even after a beatdown he decides to not Cash in.
Brock has shown before he doesn't particularly care about being Universal Champion all that much, its not some mid carder holding the case looking for there first reign for Brock the sense is its more about the game he is playing in toying with Rollins.
I'm not even sure he is gonna cash in on Friday yet, think there is still some legs to him with the case being the Constant Shadow behind Rollins back