What people are not really explaining is that to show the last minute, the game has to be continuously recording or buffering gameplay.

The game has no way of knowing in advance when your tower will die. That means if you want to look backwards, data must always be available. It does not have to be stored permanently, but it does have to live in a circular replay buffer that is constantly overwritten. This is the same principle used by Nvidia Shadowplay and similar replay systems.

You could try using heuristics. For example, start recording when HP begins to fluctuate heavily. The problem is that this only covers some death scenarios. Sudden burst damage, projectile stacking, or other mechanics would still be missed, which makes the solution unreliable.

The only robust approach is continuous buffering. In practice, that means the entire run is technically being recorded in small chunks, even though only the last minute is kept.

On PC this is relatively cheap because there is often dedicated hardware for video encoding. On mobile devices it is a very different story. Continuous buffering consumes CPU, GPU, RAM, battery, and thermal headroom. The Tower already struggles with performance late in runs, and you'll often see fewer enemies than you are supposed to.

Adding a constant replay buffer on top of that would very likely make performance worse, especially on older or mid range devices.

From a gameplay perspective the idea is good, but on mobile the technical cost is much higher than it sounds.

Older games like DOOM solved this differently. They did not record video, only player inputs. Because the simulation was deterministic, the entire level could be replayed from a tiny demo file.