It's a reasonable question - but the price can never be truly "free," because there's a cost to investment / build that product - meaning costs are non-zero. Therefore the negative profit in the short-term due to pricing is called "undercutting," as other companies (generally) don't have that luxury in the long run.

You have to ask: why is it free?

- A thousand engineers working on a non-revenue product for Google is like "pennies," when it might be a whole company anywhere else.

- How are you funding that negative profit? Using leverage and profit from strong market position elsewhere. Therefore: anti-competitive, as other companies in the space don't have similar leverage.

Now, a startup can, say, operate at negative profit and not count as "anti-competitive," because a startup most likely has fractional market share. But imagine you're building a startup in a brand new space, and Google decides to also enter that space. If you price your product at $10, and Google says "we're pricing at $0," you can imagine how no one could compete with that for the long-term. Hence why monopoly / anti-competitive rules are important.