Why was a seat left open fo Connecticut at-large?
CREATE TABLE "table1_224844_4" (
  "district" text,
  "vacator" text,
  "reason_for_change" text,
  "successor" text,
  "date_successor_seated" text
);
SELECT "reason_for_change" FROM "table1_224844_4" WHERE "district"='Connecticut At-large';