Why doesn't the WAS tell you that you're on trial or when you lose the trial?

When I was a WAS (married, 10yrs together) and "BD" was serving her D papers--
1) I didn't feel I should have to threaten my XW with divorce to get her to make the necessary changes.
2) My attorney advised against telling my XW until I'd ensured my interests were maximally protected in a divorce. Those preparations took time. Giving my spouse a heads-up would be counterproductive

When I was a LBS (3yr LTR) and "BD" was finding half my family and furniture gone--
1) She felt home life after announcing could be awkward for her daughter.
2) She wanted to ensure she landed on her feet--e.g., had found an affordable place to stay, could get her daughter moved to a local school, etc.--before announcing the end.