Many meteors break apart, disperse or burn up in Earth's atmosphere. Volatile rich meteors usually explode due to heating during the fiery atmospheric entry. Soft and crumbly chondrites would be expected to break apart often, even if they were volatile poor. Irons and stony irons punch thru the most. Meteorites found on top of the snow in Antarctica are also classified as finds.
Some finds come from rooftops and the like.
Because of all of these biases, analysts must also rely on studies performed by analyzing the light reflected off the surfaces of asteroids, and some future asteroid rendezvous missions. The only way to eliminate bias is to study the asteroids themselves. Further analysis of meteorite compositions is beyond the scope of this presentation.