Why editing some memory don't do anything

Dynamic memory don't get cleared, they are only marked as unused so if you found address that are from these unused memory they won't matter to the game when you change them.

Some memory are derived form another memory, they get refreshed by the game code before use, changing these memory only matters after the refresh and before they get to be used by the game code, which is perhaps a very small time window, this can work for those cheats that only need to be successful once, for example you only need hp to be zero once to be dead but you need your hp to always be above zero when the game code look at it to not die.