Ah ... now we are getting onto rolling versus standing starts ... I have not much concern with rolling takeoffs at high weight due to the comparatively low acceleration prior to achieving takeoff or near takeoff thrust .. but do have reservations for low weight takeoffs from short, limiting runways ...... another thread altogether ....
I don't think that rolling takeoffs is the answer you are looking for to explain the observation. There is still nothing to stop the operator building in a suitable pad to account for any rolling start losses. One longtime international operator did just this sort of thing when they introduced reduced thrust takeoffs years .. decades ... ago ... I don't know what their present attitude is.
The other problem with real BRTs is that they might tear the runway off the ground and strain it through the engine doing a static runup prior to brakes release .....
