KLM focuses on their bread and butter - Amsterdam. Similar to why BA doesn't fly to Birmingham or Stansted for example.
BA might not do STN, the same as they don't do LTN, because they already operate to/from three LON airports.
KLM Cityhopper and/or KLM Exel targeted such regional airports as EIN, GRQ, MST & RTM when they operated an appropriately sized puddle-jumper fleet of 50 seats or less, nowadays operating a fleet with their smallest sized aircraft being some 88 seats the regional airports, in KLM's apparent opinion, are no longer viable.