I agree with you about restoring backups on Azure Managed Instance being a lot faster and more predictable with Azure SQL Managed Instance. But for organizations money is king and Azure SQL Database, especially DTU-model, will allow you to save 2,000 to 3,000 dollars monthly. One thing people often overlook is that you don't pay license fees with Azure SQL Database DTU-Model.
On Azure SQL and Managed Instance the available memory for your databases is linked to the number of vcores available, the more vcores the more RAM available. Have you considered how much money will cost to scale up the tier of a Managed Instance compared to Azure SQL.
When organizations realize the savings of Azure SQL they stick with it, they find workarounds for Azure SQL limitations, and when they are reaching the storage limits, they go for Sharding their databases.
Here you will find Microsoft Documentation that compares the two products.