Could alien civilizations be too far away to contact?

Yes. Alien civilizations could be far enough away that contact is extremely difficult or effectively impossible with current physics.

Main reasons:

1. The speed of light is a hard limit
   Signals can’t travel faster than light, so even within the Milky Way a reply could take thousands to tens of thousands of years if another civilization is on the far side of the galaxy.

2. Human-made radio leakage is very hard to detect at large distances
   Ordinary Earth radio signals spread out quickly and become extremely faint. In practice, they would likely be detectable only over relatively small cosmic distances unless they were deliberately aimed, high-power transmissions.

3. The universe is expanding
   On very large scales, distant galaxies recede from us. Beyond the cosmological horizon, signals sent now would never reach each other, even given unlimited time.

4. Timing matters too
   Two civilizations also have to exist at the same time. A civilization may have appeared long before or long after another one, so their signals never overlap in a useful way.

So yes: distance, signal weakness, cosmic expansion, and timing could all prevent contact. If some form of faster-than-light communication or other new physics were possible, that could change the answer, but there’s no evidence for that at present.