Sometimes I puzzle about where you get the information for your posts.
Just because Lon Chaney did some of his famous work for the old Universal Pictures is not any indication, whatsoever, that Universal Pictures was "originally known as a horror movie studio". That's like saying that you would be wondering why Columbia Pictures made a movie like
Men In Black when they were known as the studio of the
Three Stooges shorts (which would also be a silly assertion).
Universal Pictures, as a matter of fact,
distributed the original
Balto movie, which was made by Steven Spielberg's Amblimation (just as, interestingly,
Men In Black was
distributed by Columbia Pictures, while it was filmed by Steven Spielberg's Amblin Entertainment...another of Spielberg's properties).
However, the notion that Universal Pictures was known as a horror movie studio is fallacious. They did many different kinds of movies over the years (as Balto-the-WOlf-Dog indicated). To wit:
http://en.wikipedia.org/wiki/List_of_Universal_Pictures_films