(curr_frame_tick - prev_frame_tick) is the delta time of each loop. So this value is the time it took to do the previous loop.

It doesn't increase each timestep because prev_game_tick is recalculated each step.

Step1 (initial step):

- prev_frame_tick = 0

- curr_frame_tick = 0

- delta = 0

Step2:

- prev_frame_tick = 0

- curr_frame_tick = 200

- delta = 200

Step3:

- prev_frame_tick = 200

- curr_frame_tick = 356

- delta = 156

...