The benefits of deploying SQL Server using IaaS
Besides IaaS, there is another deployment method for SQL Server: platform-as-a-service (PaaS). Azure SQL Database, or Azure SQL Managed Instance, is PaaS. With PaaS, there is no operating system (OS) or SQL Server instance you need to manage, which includes things such as patching. All of that is done for you. Where that does not work for some is that you may need control over the OS and/or SQL Server choices (version or edition) due to standards, licensing, or other requirements. PaaS provides a more packaged solution that fits the needs of many without needing a dedicated OS and SQL Server instance.
Since IaaS is just a VM with an OS, you can deploy whatever supported combination of OS and SQL Server you desire. One principal difference between IaaS and PaaS is that any automatic administration you would want done by Microsoft is opt-in, whereas PaaS is done for you and you have limited configuration choices. One important reason...