Q: Why do Rebels have so many [Letter]-Wing Fighters? In Star Wars the bigger part of rebel fighters are named after a letter, e.g. A-, B-, X- and Y-Wings.
This pattern does not carry over to fighters of other factions. (E.g. a TIE fighter could have easily be named H-Wing, but is not).
Is there any in-universe or out-of-universe explanation for these names?
I am not looking for the answer that they are called that because they look like a letter, but rather the answer to why this type of naming exists and exists only for rebels.

A:   Apparently, there is Latin alphabet in SW universe and it is called High Galactic
Therefore X-wing (officially T-65) got his name because it resembled High Galactic letter X with S-foils opened, Y-wing (BTL-.. ) resembled Y e.t.c.
Of course, out-of-universe, at the time "New Hope" was released people could only watch movie once (or few times if they really like it) and occasionally buy comics. Therefore, it would be counterproductive to bombard them with information they could not process. So Rebels had X-wings and Y-wings (easy to remember because of shape) , Empire had Tie-fighters and that was about it. Later when SW became a success and personal computers came about it was all gradually expanded. 

A: I believe that they started with one fighter, and then it was quite simple to just continue to name spacecraft after fighters. People (and aliens presumably) are creatures of habit, and they do not change established systems when it is unnecessary.

A: This is probably because of both the shape resemblance to the letter (like the y wing or t wing), and also because it is is probably a type of organisational thing for the designers, and thus easier to organise in a archive system.
