The critical period hypothesis in SLA follows a "use it then lose it" approach, which dictates that as a person ages, excess neural circuitry used during L1 learning is essentially broken down. If these neural structures remained intact they would cost unnecessary metabolic energy to maintain.
According to the critical period hypothesis in SLA, there's an "use it and lose it" principle: as people grow older, neural pathways utilized during L1 acquisition are progressively eliminated. Should these neural structures persist, they would require extra metabolic resources for maintenance.