Because there was a time when "consolidation" was the buzzword like cloud is today (cloud is still a form of consolidation...). The mantra was to run everything on fewer, more powerful systems to save money. Done in the right way it could be OK, done in the wrong way by clueless people "hey, we have this AS/400 let's run both the water control system and accounting from it! See how much we saved?" leads to these situations. Of course IBM told (and sold) you you could run different workloads on it, so why not? The AS supported hardware partitioning - but if used by clueless syadmin, little changes...
Biting the hand that feeds IT
