Most of RDBMS users don't want to use autocommit mode expecting to have a change to Rollback in case of problem.
Most of database GUI have Commit/ Rollback buttons (greyed in autocommit mode, enabled in non autocommit mode).
pgAdmin hasn't had commit/rollback buttons in nearly 20 years, and there have been very few requests to add them in that time. Would the extra space on the button bar really be worth it for most users given so few have ever asked for it?