Because it is generally accepted that monopolies are bad and that not-monopolies are ok. It is much easier to sell the simple idea that "X is a monopoly, so split X", than to make a long case that "X does Y and Z which meet ABC definition of unfair use of market position, bla bla bla, so split X". Conversely, for a company in the wrong, it is easier to say "Of course monopolies are bad, but we are not a monopoly!".

> or we really have no other words

There are other words, but it is a bit of a mouthful.

Because of these exact issues, the way that I describe the situation is usually as follows "Company X has significant market power, and is engaging in anti-competitive actions".

I have yet to have someone object to that definition.