Somehow the post vacation time always feels like a new year even more than the actual new year in January. In the middle of the winter nothing really changes, but in the autumn there is usually a lot of new beginnings. It's the start of a new school year and it's usually also when all the new projects start at work. Nobody wants to leave anything unfinished before heading off to their summer vacations.
So why do we celebrate the break of the year during the seemingly arbitrary time? It doesn't have any meaningful astronomical events happening besides winter solstice, which is mire than a week off anyway. It doesn't even have any meaningful religious occasions explaining it.
Autumn isn't the most logical time to change year either. The beginnings associated with it are rather modern. For the sake of it, it would probably make the most sense in the present day world.
The spring is where it feels most natural. It's when the nature comes back to life, start of the agricultural year. After the midwinter, the spring in fact is the most common start of the year across different cultures. Even many of those that align their start of the year during summer are often still the start of the growth season depending on the local climate.