Xenos who are legit delaying will usually find themselves without weeds, and PM'd, told "go fight, you have x minutes before you're bombed".
They usually choose to go fight so you don't see them bombed often.

Marines on the other hand usually have THINGS allowing them to delay. So that can usually be fixed by removing the THINGS they are using to delay with. Obviously this isn't always the case, just my impression for both sides.

If the situation for either side isn't untenable (read, 3 marines and a massive fort vs 40 xenos, or a lone lurker running from everything that moves without attempting to kill it) you probably won't see admin intervention.