There are three issues people could have with that:
Widespread Outages
If a popular server like AWS East-1 goes down, it seems half the internet goes offline - points out DHH.
DHH claims on the ReWork podcast that having just a few computing companies is “a perversion of how the internet was designed, which was to be fully decentralized, and very resilient. If one server went down in one place, it had no bearing on a different server, another place. And we've kind of taken that beautiful model and perverted it into this scenario where so much of the internet just runs on a handful of companies' computers.”
He imagines such a scenario “it's really not great if your project management system goes down at the same time your email goes down at the same time your documents go down. It's the same time that everything is just dark?”
Another CTO on Slack agrees saying that “the only problem I can see is that AWS, GCP, and Azure are getting too big and each failure is a real disaster.”
To make things worse - in such an outage if you don’t have a local back-up you would be waiting for “ the cloud provider to figure out what went wrong and then you'd have to wait for ‘higher prioritized customers’” writes Nils Hammar on Linkedin.
Such outages have happened in the past, but John Anthony Radosta counters on LinkedIn that extremely rare for an entire region to go down. “An AZ or service sure, but a whole region, all services? Your data center has a higher risk of going completely out than whole cloud regions do on any provider.”
So where do CTOs hold? 55% of CTOs surveyed agreed or strongly agreed with the statement “I am worried that if one cloud provider goes down, most of the internet will go down”, while 26% felt neutral about it and 18% disagreed or strongly disagreed.
One CTO wrote in the survey that although they perceive regional hosters (or self-hosting) as more prone to this risk, they do want to see this risk tackled more explicitly by the big three cloud providers.
Policing and Control
“When you concentrate that level of power with someone, you also pervert this sense of who gets to be on the internet. Which is not a major concern for us, (hopefully). But it certainly has been a concern for a lot of other people. And those mores and morals shift constantly, like who's allowed to be on the internet and who do you answer to? “ - DHH on the ReWork podcast
In a world that juggles public safety and free speech, there are cases of public computing providers denying services to some companies/organizations. Without getting into ethics and constitution, from a decentralisation point of view is this a good thing? When asked whether “It bothers me that large Cloud providers have the power to deny service at whim” CTOs were divided. Some felt that public computing companies were justified in upholding their contracts but they do think it might be risky in a monopoly. A CTO who formerly worked for a cloud computing company points out that it is not as easy to deny service as critics make it seem.
But, for CTOs of tech companies - I don’t think this will be a big problem for them from a business point of view.

Monopolies
64% of CTOs surveyed agreed or strongly agreed with the statement “It bothers me that the decentralized world we are creating will be operating on computers owned by a handful of mega-corporation”.
But as one CTO points out, these feelings are more from a personal perspective than a business perspective. The CTO continues to say “ it bothers me that AWS is cross-financing their Marketplace with the money they make from AWS”
Yet another CTO did not see a monopoly here
”There is no monopoly on this and if prices increase it creates opportunity (see Digital Ocean) etc. We‘ve rather come from extremely immature offerings (Hetzner, Telekom, etc.) to maturing technology offered by companies focusing on this business.”.
Another CTO reminds us that there is a lot of innovation coming from the hyperscalers. "It can be seen if you look at the whole serverless field. No European cloud provider is offering these services as they do not have enough innovation and capacity. However, this is also needed to provide greener services and less energy consumption."
Conclusion
Decentralisation of cloud computing is a topic of debate among CTOs. Some are concerned about the potential for widespread outages if a popular provider goes down, as well as the power that large cloud providers have to deny service at whim. Many CTOs also have personal concerns about the concentration of power in a few large corporations. However, others do not see decentralisation as a pressing issue, and argue that competition will prevent the rise of monopolies. decentralisation is a complex issue that requires further consideration and discussion.