TO BE FAIR
In the older games, the players also tended to have 4 active pokemon because two existed for the sole purposes of using HMs. It's reasonable to believe that in-universe, people would reserve a certain number for utility and only have a few trained up for battle. Or some of them may have been KO'd/been on low HP doing battles between now and the last pokemon center. It's better than the usual paradigm where the PCs are constantly low on spellcasting resources doing adventuring things while every NPC spellcaster starts every encounter with their full daily allocation.