But we don't find it hard to communicate with them, save for ideas they cannot understand. And they communicate with us. Yes, it is limited by their ability.
Scale it up...
Are you anthropormophizing? IOW, how do you know what they are thinking? Is it a trained response or does it represent genuine understanding?
Whenever I hear someone describe a motive for an animal behavior, I get very suspicious. Please don't tell me what that fish was thinking when I hooked him up- you aren't a fish. Right?
Scale it up, scale it down. What is the unit of measurement?
Does the alien being that is capable of galactic travel see us the way we see fish? Should we assume they have the same senses as us, or communicate ideas that are compatible with our understanding of things?
Why?
Are they water based? H20 is 18g/mol, NH3 is 17 g/mol. Maybe there are ammonia-based gigantic intelligent jellyfish swimming in the atmosphere on some gas giant?
Life on earth has several different patterns- maybe they are radially symmetrical? Ever have a conversation with a starfish?
You can name a few species that you believe you can communicate with here on earth- there are a great many more that you cannot communicate with, agree? My dog will fetch the stick if I say "Go get the stick!" but if I ask him to go check the mail, he just sits there and looks at me.
We assume a lot when it comes to even communicating with our pets, but how much is actual understanding and how much is trained responses is open to debate.
So say we discover an earth-like planet, and it has life on it. What are the chances that it is similar enough to us to make communication even possible? The only thing I have to go by is life on earth. On earth, there are many species that evolved in parallel with us. Very few of them are ones we can communicate with at any level, and when we can it is extremely basic, and only after a lot of effort.
When I think of communicating with aliens, I first consider our ability to communicate with species that are not alien, and I find that is not very easy to do.