Indeed ASUS phones must fully support the carriers of the country they sell the phones to. They don't do that now & they're getting away with it. Unethical!
E.g., in Australia, they don't support VoLTE/VoWiFi features right out of the box for any of three carriers -- Telstra, Optus & Vodafone. For comparison iPhones supported those features from 2014. It's a fair assumption that an ASUS phone released today, i.e., some seven years after that iPhone, would support those features, but unbelievably they don't. If they can't even implement the kind of yesteryear's 4G features that are so prevalent even amongst ~$300 (AUD) phones, what hope is there for any 5G features?
I'm seriously regretting buying Rog phone 5 & realising a while later that it doesn't support VoLTE/VoWiFi. Those are essential feature for any phone at my workplace where 3G signals are too weak to make & receive calls, and with Rog phone 5, I'm missing out on important calls. I was going to praise this phone to high heavens & recommend it to friends and colleagues. Instead, now that I've been badly bitten by it, I'll be influencing whomever I can against buying it. Once bitten twice shy: I won't be buying an ASUS product again nor would I recommend them in good conscience to anybody.
It'd seem by their attitude of lethargy and carelessness they're simply busy in driving away their existing customers & future potentials.
As a departing advice for ASUS, let me say this: Whichever the market you're selling your products to, do implement all the essential features a phone needs in that market this time and age. Don't let lethargy define your company. Or as a definite positive alternative, be honest & declare upfront in all of your marketing and sales materials what essential features your products lack (viz., VoLTE/VoWiFi) compared to your competitors, so that a customer can make an educated decision up front. At least you'd then have one less disgruntled customer that way. Thanks.