Bran couldn't Warg into Hodor because he was already warged into the past, so his only way to have Hodor save the day (present time) was to intentionally program Wylis "hold the door" until that moment came, well knowing that Wylis would be damaged for life. Well that's my two cents.

Bran couldn't Warg into Hodor because he was already warged into the past, so his only way to have Hodor save the day (present time) was to intentionally program Wylis "hold the door" until that moment came, well knowing that Wylis would be damaged for life.