I work in this industry(though thankfully very rarely directly with SAP) and I cannot fathon why it is popular either. As I explained in my other answer in this thread, everything they touch turns to garbage.
I think it's really a case of a self-fulfilling prophecy, of a sort. They are the biggest in the business, so people go with them, which makes them bigger, which attracts people.. and so on. It probably helps(SAP) that they also decades worth of man-hours implementing all sorts of insane business logic(like for accounting, as you mentioned, which is something you definitely don't want to get wrong) where other players are likely to be behind.
I think it's really a case of a self-fulfilling prophecy, of a sort. They are the biggest in the business, so people go with them, which makes them bigger, which attracts people.. and so on. It probably helps(SAP) that they also decades worth of man-hours implementing all sorts of insane business logic(like for accounting, as you mentioned, which is something you definitely don't want to get wrong) where other players are likely to be behind.