If TLJ got one thing right its no one coming to the Resistance's aid when Leia called
If I saw the Empire II just wipe out the entire government in a single attack, the last thing I'd do is get involved in any of that.
If, in TROS, some random guy would then be like "hey Palpatine is somehow returning, we need everyone in the galaxy to come across the galaxy through this dangerous path to an ancient evil sith planet on a suicide mission against the boss of the people who just killed five planets", then realistically no one would come help and just assume "eh it'll probably work out, I really don't want to face certain death"