CREATE TABLE table_25039 ("District" TEXT, "Vacator" TEXT, "Reason for change" TEXT, "Successor" TEXT, "Date successor seated" TEXT)

Why was a seat left open fo Connecticut at-large?
SELECT "Reason for change" FROM table_25039 WHERE "District" = 'Connecticut At-large'
SELECT "Reason for change" FROM "table_25039" WHERE "District" = 'Connecticut At-large'