Part of selling a product, any product, is trust in the product. At a most basic level that something will do what it says it will do.
On a wider scale brands are valued and charge a premium because of trust. Trust that a product or service will be supported and will continue over a period. Of course there is “end of life” when new products replace it and occasionally a product that just wont sell and makes no sense in continuing. Customers understand that. However the brand trust will get over that.
Suppose now Microsoft comes out with a SurfacePhone. Who now trusts Microsoft with first party mobile devices? They spent $7.2 billion dollars on a first party mobile brand and ditched it. They have rebooted their mobile operating system 3 times since 2010. They have changed their development strategy to UWP which no one uses. They have an app free mobile platform with little to think it changes.
You can even buy your Samsung Galaxy S8 from Microsoft Retail Stores.
If the SurfacePhone is launched at $500, $600 or more then what consumer doesn’t look at that price point and think about spending their money. How does a consumer trust that Microsoft is really interested in Windows on Mobile. So far the evidence is that Microsoft are totally dis-interested. They would like a successful mobile product but in the vast size of Microsoft businesses it’s just another thing.