[atomicnumber3]

A couple, but they're all "human" reasons and not really technical. The TLDs records will be served off the gTLD nameservers like everything else, you can change your own nameservers from there, and DNS is slow as hell anyway (by modern standards) so it's already not like it's tightly optimized usually, and performance as perceived by the end user is greatly predicated on how warm their cache is. So any performance difference between nameservers probably barely matters unless you're like Amazon or something.

Anyway, non-objective reasons I can think of:

Lots of people don't know anything but com exists.

Com is definitely still dominant, so someone sitting on yourthing.com when yourthing.biz.no is your real site will probably be getting some chunk of your traffic. Imagine if Amazon.co.uk was the real Amazon and Amazon.com was like, a news website dedicated to posting all the bad stuff Amazon does. Tbh that'd be nice for society but you can probably understand it would be undesirable for a company.

.io is one of the only ones that's managed to kinda read com-like status, and it's only for a niche (though a lucrative niche!) audience.

[Macha]

> Imagine if Amazon.co.uk was the real Amazon and Amazon.com was like

This is actually an interesting example, because Amazon.com is a US/Canada specific site, while Amazon.co.uk is the UK/Ireland site (though I'd imagine they'll eventually either set up an Amazon.ie or change the redirect to Amazon.de with the tax/import brexit implications of that). So while all domains are Amazon owned, I wouldn't say Amazon has .com primacy over regional domains.

Ditto for google search, though the rest of their products are on google.com for me (I think gmail used to be googlemail.co.uk in the UK and googlemail.de in Germany because of local companies who had the gmail name first, until Google bought out the names from the local owners).

All the web 2.0 or newer companies are .com rather than regionalised though.