Well it's tricky. I don't really have a problem with google owning the .google TLD, because that is a pretty unique name, and is unlikely to be useful for anything besides unrelated to Google. Similarly for .walmart or .microsoft. But .apple is a problem, because it is a common English word, and it isn't unreasonable for say an apple orchard, or an apple cider company to want a .apple domain. Similarly for other brand names like target, zoom, uber, plaid, etc. Even .amazon fits here since it is also the name of a river, a rain forest, and mythological group of women.

But where do you draw the line? How do you decide if a company should be allowed to get a gTLD for their brand? Clearly, having a trademark is not sufficient, as it is possible to get a trademark on a common word, and it is possible for multiple companies to trademark the same word as long as there isn't a risk of confusing them. Is it fair to let google and microsoft get such TLDs for their brands, but not apple and amazon?

Is it tricky? If you have a trademark, you can have a gTLD - simple as that.

Because the problem is how can apple have a trademark on the word “apple”?

For me, the same rules should be enforced for trademarks because an apple orchard might also like to have a trademark but that’s difficult because “apple” is already a trademark.

Edit: as pointed out in the comments, this position doesn't take into account that trademarks are very much national and cultural.

Perhaps one day gTLDs will become free (once the gold rush is over) just as SSL/TLS certificates did with the arrival of Lets Encrypt.