this is a question so many people have asked me now. i might have a few thousands of them now. think im finally going to answer it.
when i made my first blog i used this picture as a background. the blog i used it for was ask-celestia-stuff (short neck) and i only had one post that only showed the head. when i showed the picture to the people who was following me from my other blog they sendt alot of questions about the long neck of the celestia in the background so since it was the most requested thing to answer i drew my second update with celestia with a really long silly neck
the background was inspired by another celestia blog i was following at the time named ask-selestia-and-runa. its a really cute blog and i really love it and it had long necked celestia a long time before me so i guess you can thank her/him for the neck comedy
so yeh. thats pretty much it. the reason celestia has a long neck.