Because the impact on your code by going with a serverless platform. Generally speaking if it's the platform you have you will shoehorn the shape of your code into a serverless shape bucket even if it has no business looking like that. These architectural shortcomings will inevitably come back to haunt you. Also most of these platforms amount to cgi-bin v2, meaning things like memory leaks and requests that hang get swept under the rug. Meaning you already have very difficult to diagnose failures and when you do eventually go to migrate you will find your code is full of these smells making it harder to reform into something reasonable.