The ones that crash are just the tip of the ice berg. The ones that land and abduct and evade our notice must be huge. Think how many flights there are around the world vs how many crashes. Earth must be a busy research/holiday destination for aliens.
Holiday. You think a civilization capable of FTL would need to physically probe an organism to study it? Hell no. Probing is a huge laugh. Heck, we do it to each other, constantly.