I believe it has to do with the fact that the US possesses a vast amount of land, abundant natural resources, a long-standing democracy, no wars on its territory for an extended period, and a relatively large population size.

If you compare that with other wealthy countries such as Germany, then you'll see that they have less land, fewer natural resources, haven't had democracy for as long, were divided until the late '80s, and do not have as large a population size.

Therefore, just by sheer numbers, it makes sense that everything in the US is bigger. Moreover, Germany, for instance, has a culture where wealth is accumulated across a large number of medium-sized companies, whereas in the US, wealth is increasingly concentrated at the top (for example, the ones you mentioned). These are, of course, the entities everyone knows and talks about.