Is there any good reason to write "it is easy to see"? Many academic papers, particularly in mathematics and similar fields, use the phrase "it is easy to see that..." (e.g. in a mathematical proof). I never understood why this sentence is used. Such a sentence is inaccurate at best, since it is not easy for everyone to see; maybe it is easy for the author or some of the readers, but there are certainly readers to whom it is not easy. 
Authors often try to shorten their paper as much as possible, so it is not clear why they would lengthen their paper by an inaccurate sentence.

Is there any good reason for an author to use this phrase?
Mathematical papers, especially, and many others, are not written for the complete novice with no understanding of the field. One tries to tailor the explanation of a new concept to the general level of understanding of the audience and tries to avoid being overly pedantic giving every detail and argument back to Euclid. 

College lecturers often use such phrases, knowing the level that their students should have attained and, thus, permitting the lecture to flow more smoothly and be less boring. 

But writers do the same thing, envisioning the reader of the paper, or perhaps just the reviewers. If I say such a thing and the reviewer calls me on it, then I know I have to say more. But I trust that the reviewer can validly stand in place of the audience and will be able to easily fill such gaps. 

When such a phrase is used (we can conclude X) it implies that X flows from the previous statement(s) and isn't just an unsupported statement inserted into the flow. It indicates a hopefully simple, but unstated, argument.

The alternative of including the complete argument is longer, more pedantic, more boring papers. 

The other alternative of starting every sentence with "Therefore,..." is also stilted and, eventually, boring. Some variation of phrasing makes the reading more pleasant. Writers, in general, like to have a repertoire of, more or less, equivalent phrases to help the flow. 

On the other hand, it has happened that the statement is used incorrectly when it takes a lot of argument and deep insight to go from point A to point B. Sometimes the author just doesn't notice the width of the gap. But, for the most part, it seems to work out.