Its convenient linguistic shorthand for a common case which would be more properly be described as “a concept of a thing which does not correspond to any actual thing”. While the equivalent linguistic shorthand has been present in most languages for quite a long time, the recognition that the confusion it can sometimes produce between concepts and concrete things is a category error is, while not nearly as old, also fairly old; it is central to Kant’s argument against the ontological argument for God’s existence, for instance.

And why shouldn't we go with the convenient linguistic shorthand instead of the esoteric ontological argument?

> And why shouldn't we go with the convenient linguistic shorthand

Who said you shouldn't? The shorthand is convenient. But it doesn't mean what other statements with the same shape mean. A thing which isn't doesn't have a state or representation.