Some of it is probably institution dependent also... Our trauma team wants and expects FAST exams "most" of the time, even on the hemodynamically stable patients. If you don't do it, and send the pt to CT, they moan about not being told about the positive FAST prior to going to CT. If you do it and they are stable, then again..."most" of the time, they get the CT anyway before making any operative decisions. Either way, from my perspective... more information is never a bad idea although I'm not arguing for a FAST in every patient, but as I said, I think there's always the potential...such as the cases that I mentioned, where it has the ability to change management. My 2 cents, but then again... I'm a proponent of US. I think it's an underused diagnostic modality for the most part.
In your defense, there have been quite a few 2 papers off the top of my head in recent years arguing against the utility of a FAST in exactly the type of cases that you are describing. I don't agree with those papers for reasons beyond the purpose of this thread, but to me, if there's room for argument without a clear consensus, then that's not a reason to stop doing it. Especially when eFAST is obviously being pushed forward in ATLS guidelines as an adjunct to the primary survey.
Of note... there's more than a few studies showing better sensitivity of detecting both PTX and HTX with US vs CXR. With PTX something along the lines of 88% vs 52% in a 20 study meta. If I know they have PTX from my eFAST, but don't have clinical evidence of a severe PTX, I'd probably ask for a cross table lateral along with my portable, knowing that seeing a medium anterior PTX on supine portable is not going to help very much. Would it change my management? It did in ordering the cross table lateral CXR, but from that point? Maybe, maybe not...
Anyway, I hear ya. Just my 2 cents.