Technology

You can return multiple A/AAAA records for the root, the TLD delegates the whole thing to your nameservers and it's free to return whatever you want. Registrars actually do let you set records on the TLD's zone, it's called glue records and they're typically used to solve the nameserver chicken and egg problem where you might want to be your own nameservers. Mine's set that way:

~ $ drill NS max-p.me
;; ->>HEADER<<- opcode: QUERY, rcode: NOERROR, id: 32318
;; flags: qr rd ra ; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;; max-p.me.    IN      NS

;; ANSWER SECTION:
max-p.me.       3600    IN      NS      ns2.max-p.me.
max-p.me.       3600    IN      NS      ns1.max-p.me.

The me registrar will give you the IP for those two so you can then ask my server for where max-p.me really is.

The bigger issue is usually there's a bunch of stuff under your root domain like MX records, TXT records, potentially subdomains. That's a huge problem if you need to CNAME the root to a hosting provider, as the CNAME will forward the entire domain including MX and TXT records. Cloudflare sort of works around that with server side flattening of CNAMEs, but that's not standard. But if you have a www subdomain, then it's a complete non-issue. And really, do you want to delegate your MX records to WP Engine?

The main reason people went without the www is the good old "it looks cooler and shorter" while ignoring all the technical challenges its brings, and that's probably why browsers now hide the www so that website designers don't have to do this atrocity.