Answering this seriously, id say its the fact that neither one really faltered/backed down from the ship unlike the other HoloEN ships. Ame didn't want to be seen as a sidekick, Mori went too hard on being "tsun" on top of not really taking Hololive seriously until later, Kronii's comment on shipping just being for fun broke the illusion, Shiori just makes some sex jokes to play along but can be too brutal wording and its obvious she's not really into it. Baerys is in kinda a weird spot where they can flip flop in being a ship or not due to them going for a divorce dynamic.

Also, its not like its that limited to HoloEN, a number of HoloJP ships have pretty much sunk when one or both started to want to "distance" themselves from it.