It's a classic catch-22. Citizen developers can create their Flow's and while the person who built it remains in the company and/or the scope of their use is within a team, then if they do have a problem with credentials, then the impact is small and probably acceptable. But, as soon as you try to scale to a larger number of users or build recurring flows, then that's when the need for a service account seems to manifest itself.
But, many companies are struggling to understand all the products in Office 365 and the governance needed to administer and safeguard them all effectively. So, in my experience there is a real concern around enabling Flow (and PowerApps) licenses for the people who can best prove their value.
If you then add the need for a service account into the mix, especially post-GDPR, then what started out as a simple productivity solution becomes an exercise in frustration. Theoretically the Flow could be exported by the citizen developer, imported using the service account, and then re-configured with new connections. This is all easily done, but it's very hard getting any of this to happen without high-level support for it.