The reason for this is the following：

Running memory refers to ram, which is equivalent to the memory bank of a computer. It is a chip on the motherboard, and the capacity cannot be modified.

The running memory occupied by the system after root does nothing and nothing will change.

If some system programs are frozen/uninstalled after root, and some background programs are prohibited by using software such as greenguard, the available running memory will increase.

If you use virtual memory swap software after root, you will get more virtual memory, which can increase the number of multi-tasks to some extent. However, the speed of virtual memory is extremely slow, which can not effectively improve performance.