Trouble is, real experts are thin on the ground.
SAP is unlike any other skill in the IT sector. There are so many modules, flavours and niches, that it's hard to work out what you actually need.
And, when you do know, there's the bigger challenge of finding somebody who's available, affordable, and a good fit with your culture. All assuming they don't get snapped up by somebody else in the meantime.
It's like hunting Zebra Unicorns.
With SAP recruiters, your only contact is through timesheets or sales calls. SIs are expensive and concerned with making themselves sticky, breeding like cockroaches around your water coolers.
Resulting's model is a little different...
Which is why both clients and consultants choose to work with us time and again.