1) It’s hard. It takes a great deal of time to thoroughly and effectively map your processes, and requires a high degree of input from knowledgeable people. Despite the sales pitches from consulting companies, it’s not as easy as unleashing a bunch of consultants with clipboards and leaving them to their own devices.
2) Initially, it’s hard to quantify an ROI. So you’ve mapped all your processes, so what?? Where BPM actually becomes relevant is when you take your new found understanding of how your business works and refine your operations through any number of optimization methodologies, in/out sourcing, geographic relocation, etc.
It’s a bit like training for a marathon. You do all this work (BPM) that really doesn’t provide any return until you run the race (process improvement) and get your medal.