I wonder if they want to prevent reselling or at least require that it goes through their app? (I think this is a bad thing for them to do, just trying to think of the motivation).

The code is rolling so you can't use a screenshot to enter the show. This is to stop ticket transfers outside the system.

The ticket stub is animated so you can't use a simple screenshot to move to a better location once inside the show.

Human beings are checking those tickets, and movement is proof of liveness (and not a screenshot you and 25 friends are sharing). Many ticket checking systems are not connected to the internet and cannot/will not check if it's already been used. Many of the motion enabled codes are also basically working in the same way as 2FA codes: your ticket is given with a public key, usually unique to your device, and rotates every minute. Allows them to ensure that the ticket is up to date, not forged and signed properly.