If you know which DNS names you will need to know, then yes, there's no need for more than a hosts file.

Until DNS changes.

If I move a server from one IP to another, I change DNS, and in $TTL time everyone's pointing at the new server. Apart from you with a hosts file. How does that work if everyone has a hosts file?

If I say "check out this interesting story on blahblah.com", you don't have it in your hosts file, how do you get it?

I maintain a list of every phone number I am likely to use on a repeated basis, but sometimes I need to look up a phone number I don't know (in the old days this was a phone book locally, and directory inquiries further afield. Now it's ddg and assume they have a website. Which isn't in my hosts file or dns cache, and I've never visited before)

I maintain DNS entries for my home network of a dozen devices -- I host it on my mikrotik, but it's handy to have, when I type "ssh laptop" rather than remembering if it's on .71 or .73. It's one step better than a plain text file, as there's a standard based way to remotely query it. At work I maintain a DNS server with 2000 entries on my network, which is actually hosts file powered, but again I use dnsmasq for the DNS server rather than rsyncing that hosts file to 2000 machines.