It depends on the setup. Some cloud load balancers like AWS ELB require a CNAME, which DNS (RFC 1912) doesn't allow other records at that level if it has a CNAME.
So, can't put a CNAME on the apex, which probably also has MX records. I think in some cases like Exchange, if it sees a CNAME, it doesn't bother with looking at the MX.
Back in the day "CNAME flattening" or aliases (RFC draft draft-ietf-dnsop-aname) wasn't a common thing, so only real way was to redirect the domain apex to www, and then use a CNAME on the www. You'd probably need a separate service/servers to handle that redirect (at least DNS round robin would work in this case). So yea extra complexity in that case, due to the requirements. Or, give them DNS authority (eg, AWS Route 53).
Then there's the whole era of TV/radio commercials telling people "www dot <name>" that a lot of people type it anyways. You can redirect www to apex, which some sites do for a "clean brand" but now browsers are dropping the www in the UI anyways.
I've also run into plenty situations where www worked but apex didn't. Relatedly, it's a little surprising that browsers didn't default to assuming typing the apex in the browser it would try www first. And recently, now we're getting SVCB and HTTPS DNS RRs along with A/AAAA (and maybe ANAME). Indeed lots of complexity.
So, can't put a CNAME on the apex, which probably also has MX records. I think in some cases like Exchange, if it sees a CNAME, it doesn't bother with looking at the MX.
Back in the day "CNAME flattening" or aliases (RFC draft draft-ietf-dnsop-aname) wasn't a common thing, so only real way was to redirect the domain apex to www, and then use a CNAME on the www. You'd probably need a separate service/servers to handle that redirect (at least DNS round robin would work in this case). So yea extra complexity in that case, due to the requirements. Or, give them DNS authority (eg, AWS Route 53).
Then there's the whole era of TV/radio commercials telling people "www dot <name>" that a lot of people type it anyways. You can redirect www to apex, which some sites do for a "clean brand" but now browsers are dropping the www in the UI anyways.
I've also run into plenty situations where www worked but apex didn't. Relatedly, it's a little surprising that browsers didn't default to assuming typing the apex in the browser it would try www first. And recently, now we're getting SVCB and HTTPS DNS RRs along with A/AAAA (and maybe ANAME). Indeed lots of complexity.