Deep Singh

Whenever I seem to read about tuned Evos or Skylines they hardly ever seem to have fully mappable ECUs.The last few issues of Banzai/Jap Perf I've read some quite big BHP(I know sometimes exaggerated) Evos and Skylines all using boost and fuel piggyback computers.The owners have'nt skimped on money because they've installed hybrid turbos,uprated fmics,oil coolers,complete manifold systems even some internal strengthening etc but then decided not to go down the route of stand alone units.Why d'ont they want/need control of ignition aswell with all that extra hardware? Spud you out there?