Large scale - in some things - allows for higher quality at lower prices since you divide the costs of designing and building between more people. For many complex things you have to be a large enterprise to build it. Building a reliable engine that meets modern emissions standards isn't possible for a single human, or even a small group - a large (monopoly) can make that investment and divide those costs between many customers and so the price is cheaper than a small company that would have to divide the costs between many less customers. Tech tends to be similarly complex and so needs are large investment in R&D to be acceptable, which in turn means that they need to be large to make the costs divided between all customers acceptable.
The real question is where do those competing considerations meet up. A monopoly is bad, but you can go too far in the other direction as well. I don't know how to decide what the best answer is (I'm not even aware of anyone who has made a useful argument for any particular compromise)
Those things are not linked. Large and monopoly are very different. Your example of engines is good, there isn't afaik a monopoly on building engines. Even a small number of huge auto makers are still competing against each other.
> A monopoly is bad, but you can go too far in the other direction as well. I don't know how to decide what the best answer is (I'm not even aware of anyone who has made a useful argument for any particular compromise)
I agree, I think the general aim with the EU makes sense which is about use of power in one field to control another. So google are good at search but that doesn't mean they get to make their own shopping attempt rank higher than others. If they have 90% of the search market then fine if that came from being better than everyone else but their shopping offering has to be better than others.
The real question is where do those competing considerations meet up. A monopoly is bad, but you can go too far in the other direction as well. I don't know how to decide what the best answer is (I'm not even aware of anyone who has made a useful argument for any particular compromise)