Quasars existed billions of years ago when the early Universe was filled with much more gas and dust. These quasars are very massive objects (full of gas and dust) which are powered by blackholes (gravitational force at center is enormous). But a lot of the gas clouds have been already converted into stars (and later radiation) there is little stuff left to form quasars. That is why we don't see many around today. A galaxy cannot evolve into a quasar unless it could somehow absorb a LOT of matter. Hope that helps.