When Salesforce announced this week that it was moving Marketing Cloud to Microsoft Azure, it was easy to see this as another case of wacky enterprise partnerships. But there had to be sound business reasons why the partnership came together, rather than going with AWS or Google Cloud Platform, both of which are also Salesforce partners in other contexts.

If you ask Salesforce, it says it was ultimately because of compatibility with Microsoft SQL.

“Salesforce chose Azure because it is a trusted platform with a global footprint, multi-layered security approach, robust disaster recovery strategy with auto failover, automatic updates and more,” a Salesforce spokesperson told TechCrunch. “Marketing Cloud also has a long standing relationship with Microsoft SQL which makes the transition to SQL on Azure a natural decision.”

Except for the SQL part, Microsoft’s chief rivals at AWS and Google Cloud Platform also provide those benefits. In fact, each of those reasons cited by the spokesperson — with the exception of SQL — are all part of the general cloud infrastructure value proposition that all the major cloud vendors provide.

There’s probably more to it than simply compatibility. There is also a long-standing rivalry between the two companies, and why in spite of their competition, they continue to make deals like this in the spirit of co-opetition. We spoke to a few industry experts to get their take on the deal to find out why these two seeming rivals decided to come together.

Retailer’s dilemma

Tony Byrne, founder and principal analyst at Real Story Group, thinks it could be related to the fact it’s a marketing tool and some customers may be wary about hosting their businesses on AWS while competing with Amazon on the retail side. This is a common argument for why retail customers in particular are more likely to go with Microsoft or Google over AWS.

“Salesforce Marketing Cloud tends to target B2C enterprises, so the choice of Azure makes sense in one context where some B2C firms are wary of Amazon for competitive reasons. But I’d also imagine there’s more to the decision than that,” Byrne said.