At this point the reason to allow them is because they already did and they shouldn’t break links unnecessarily. I guess another reason is because they allow nonsense like .google now so what’s the actual harm in a country having two or three?
For things like `pki.goog` or `ecr.aws` I think it makes a lot of sense; compared to an equivalent .com domain it removes the Verisign dependency from the DNS resolution chain.
Companies also always "need" the .com (and country, TLD) as people will always try companyname.com.
New TLDs work for some people's blogs, some places with more technical audience or specific marketing campaigns.