It’s an interesting scenario. Your wheels touch the ground; you engage reverse thrust and it instantly fails; you are rolling at dangerous landing speed but now can’t go around?
Relatedly, I wonder why did the pilots not engage the regular brakes ASAP.
Not quite, reading around it seems that flight planning requires you to assume that reverse thrusters and ground spoilers don’t work.
So you land, your reverse thrusters immediately fail, and you’re now required to stop using your manual breaks and consume all of the breaking distance you originally planned for, with presumably a bit of margin on top.
Relatedly, I wonder why did the pilots not engage the regular brakes ASAP.