They probably do. I think there are two possibilities: either life is so rare that in order to spawn from seemingly nothing you need a whole host of viable circumstances such as being in the Goldilocks zone, massive amounts of time, and a whole lot of luck etc., and so it has only occurred in one place (Earth); or life pops up everywhere it's able and the universe is teeming with life (perhaps even on moons such as Europa).
If the latter is true, then as for why we've encountered none or any signals is because space is vast, much more vast than many think or can imagine. Our signals haven't barley even traveled any distance yet!
True. But where are their signals then? Where are their spaceships? If life is so abundant it probably first appeared long ago. Long enough for some aliens to explore and expand throughout the universe. But we see nothing like that. Maybe the dark forest has it right?
https://en.wikipedia.org/wiki/The_Dark_Forest Or maybe aliens are already here:
https://www.nytimes.com/2017/12/16/us/politics/pentagon-program-ufo-harry-reid.html if this isn't just another way for politicians to funnel money into their rich friends' pockets.
On the other hand is asking where the alien spaceships are like asking where their horses and carriages are?