Nearly half isn't enough to trigger antitrust. Especially because that nearly half is only mom and pop shops and not the ones doing the real big business. So I wouldn't be too worried about that.
So, while you're right - online publishing doesn't have popular mindshare - it is a massive part of the online economy.
I'm not saying that qualifies WP for anti-trust investigation, but your underlying premise that WordPress is irrelevant is not congruent with reality.
From an internal tablet tool for sales reps, to the entire help system for an MS product that got translated into iirc about 100 languages, to a shareable library of B2B solutions, I’ve not once worked on a WP project that was a blog.
For competitors, on the small scale side, you have Wix/Squarespaxe/Weebly. Or just Shopify for e-commerce. For enterprise, Adobe experience manager is huge. Loads of places just write their own website and have their own CMS solution.
So no, it doesn’t even come close to having a monopoly on anything. And even if WordPress did, no individual company does. There are a huge number of different companies competing in the WordPress hosting space. Automattic doesn’t even host that much (https://w3techs.com/technologies/details/ho-automattic)
Section 2, which covers "Every person who shall monopolize, or attempt to monopolize, or combine or conspire with any other person or persons, to monopolize any part of the trade or commerce [...]" has been found by courts, I believe, to require 50% market share (or sometimes more) to apply.
But section 1, which applies to "Every contract, combination in the form of trust or otherwise, or conspiracy, in restraint of trade or commerce [...]", does not as far as I've been able to tell have any market size threshold.