That's not true though. Cloud vendors can choose to pay Redis Ltd to continue to offer "official" Redis as a managed product. Azure is doing this. AWS and GCP just chose not to.
Even if Azure Redis is cheap now, just wait until the next low-performing quarter at Redis Ltd, and they'll raise Azure's fees to make their offering more attractive.
They are the monopolist now, no one can force them to have fair prices.
Cloud vendors can also offer better inter-op between their managed Redis product and their other managed services, availability of managed Redis in every single region the cloud vendor offers, lower latency, etc. The managed offering directly from Redis Ltd can't compete on those qualities.
Additionally, Redis Ltd is motivated to not massively jack up fees on Azure, because in that situation Azure could switch to ValKey (or any other fork, or an in-house compatible re-write -- which they already have one of) and tell Redis Ltd to pound sand, like what AWS and GCP did.
Market forces are what makes Redis Ltd have fair prices, and this inherently means there's no monopoly.
They don't want to use big (especially US) cloud hosters.
Funnily enough, it also means most of those "buy hosted only from us" setups with hashicorp or redit are also dead in the water.
So it's build from scratch or fork or go for project that has clearer leadership on what it's for and isn't going to rug pull.