They have you go through each phase in “blocks”, and by the time your next season starts, you’re supposed to be bigger, stronger, and faster.
… but it doesn’t always end up happening.
The problem here is -- when you train in segmented phases like this, you end up losing the improvements you’ve made from each phase at the end of the program.
By the time you’ve hit the speed and agility phase, the gains you’ve made from the hypertrophy and strength phases dissolve away, because there’s no more stimulation in those rep ranges.
It truly ends up being a case of “if you don’t use it, you lose it”.
What you need to use instead, is something called “concurrent periodization”.
This is where you’re training all three phases simultaneously -- so that you continue to improve in all 3 “training zones” at the same time, and at the end of the off-season, you’ve kept all the gains you’ve worked so hard for.