The idea behind the Shuttle was "disposable parts are cheap, everything expensive is recovered" - in particular, the three highly advanced engines, plus their systems. The huge but simple fuel tank was discarded. The intent (although not realized) was immense reduction of costs per launch due to heavy reuse of the components.
Buran didn't carry the engines - it was strapped to a disposable Energia launcher, with disposable liquid fuel boosters, and I don't really see any obvious advantages (present, or intended but not delivered) over non-recoverable designs. Maybe it would possess the capacity of recovering satellites from orbit (although I never heard of such intent in relation to Buran) but that's a minor advantage and I doubt it would be worth the expense. So - why?