This is one of the places that "do one thing" principle breaks down. Or a bad habit became a bad definition for the use case of a command and it stuck for newbies.

`cat` usually does one thing: concatenate the contents of the inputs you give in the order you give them. Of course, if the user gives only one input, it will only print that.

It is not a text viewer even though many *nix users use it that way because they learned it that way, because a series of tutorials taught the wrong thing to generations. The very first one probably came from a very limited and very bad Unix environment like a server that is hostile to active development. So the tutorial used whatever core utility that's available: cat, beginning the multi-generational bad habit.