I don't really understand - it's googles product (phones, search, etc) why can't they do what they like with it? I'm sure people would go elsewhere if other products were any good?
Because it doesn't affect the person searching if Google's results don't show correctly the most popular results, it affects the company being pushed down the rankings - and the person searching is the person with decision-making power.
- Person A searches for "maps", either on the site, on the phone or on Chrome.
- Google promotes their own maps to the top regardless of whether they're the best choice, ahead of company B's solution, whether that solution is better or not.
- Person A sees that Google Maps is top and assumes they're better than company B, as you would when looking at a link in the #1 spot.
Company B's previous recourse was basically, to live with it - Google have control over the entire stack, top to bottom. Companies can't go elsewhere because Google index them, not the other way around, and Google keep how they calculate popularity hidden, so SEO for them is a combination of guesswork and research (costs which Google don't have to pay, incidentally). It's therefore up to the searchers to go elsewhere to get search results, but because Google are trusted to provide the correct answers, why would people do that? It's not the user's fault that Google dishonestly reports their results as the best even if others are better, it's Google's.
Anyway, in Europe it's against the law for Google to act in that way considering their position as provider of 66% of searches, so it was challenged. Google's solution in response to that legal action was to allow companies to pay Google to be promoted to top spot, but companies (naturally) thought that it was unfair that they would have to pay for equal consideration when Google do it to themselves for free. Now they have to come up with another idea.