When you write it like that it kind of makes sense. Cloud offerings tend to be fixed in a certain pattern or deployment, typically this is to achieve a level of commonality and consistency. This consistency is where some of the cost benefits of cloud come from.
However, in the absence of mature and widely supported interoperability standards then joining two or more cloud infrastructures together is actually quite hard. Each provider has their way of doing things and their own supported standards for non-functional areas such as service level agreements, user management, network connection security and service management reporting.
For instance, trying to obtain a single service management dashboard view of a system that is split between two cloud providers is quite hard. I found that it involves bespoke design and some negotiation to work out how to get system and security events out of the cloud and into a system’s central service management incident desk tooling.
Some cloud providers don’t do infrastructure events and only offer service management events at the application level. This opacity means there is a level of trust (and SLA management) that underlying infrastructure events will be managed before they impact the application. That platform management as a service is what you pay for of course. However you do risk losing some of the early warning indicators that might impact an application’s availability for it actually impacts the application.
On reflection, it sometimes feels like that cloud integration today is similar to how packaged application integration was like 15 years ago. Back then, each package had its own way of doing things and a fairly restricted set of APIs to allow access to non-functional capabilities.
The good news is that I think cloud integration will catch up quite quickly as the general integration challenges have been solved in the recent past and the SAML, SNMP, VPN, LDAP, etc standards and patterns all exist. We just need to wait for the dust to settle as different vendors agree on the same standards and patterns between them.