It's so much cheaper and faster already today that it makes sense to do v6-only internally and deliver IPv6 to the large fraction of customers who can have IPv6 and deploy a transform layer for the (gradually shrinking) class of have-nots.
Your IPv4-only competitors are spending more money to deliver a worse service. Maybe they'll wake up and realise, but the story of the past couple of decades suggests most such outfits are not too bright and when offered IPv6 on new links they'll smugly decline. Meanwhile you get to keep the difference. Your competitor thinks this service costs 86¢ per dollar revenue and you're only spending 84¢ per dollar revenue that's a lot of extra profitability.
Fighting this is a losing battle, and I imagine that decades from now somebody is going to write a book about how it was cognitively possible for "leaders" to champion an idea that couldn't possibly work, that they intellectually knew couldn't work, and all the actual evidence said wasn't working, and yet they believed in it anyway. Or that book might be about climate change denial, either way.
Eventually by the way - and 90% global is close to and even perhaps at the threshold where that's plausible for some of them - many general ISPs won't bother providing actual IPv4 networking. If you want IPv4 you're a niche customer, go find a bespoke IPv4 Internet Service Provider. If you're IPv6 capable but you want to reach an IPv4 host you'll go via a translation box automatically. As the interest in global IPv4 shrinks, the transit companies will lose interest in that service too, and eventually - decades from now - the IPv4 Internet literally goes away, the RIRs stop "managing" the now largely unused space and the residual pockets of IPv4 cease to interoperate.