Not disagreeing with you. Somebody posted the usecases below (https:/www.peachpie.io/usecases). The most common usecase is basically a legacy site in PHP that wants to/has to migrate to .NET. Reasons can include connecting PHP to .NET modules, performance enhancements, security issues that .NET doesn't have to worry about. There are other possible usecases though, like producing/consuming NuGets from PHP codes, distributing PHP apps sourcelessly, being able to run PHP apps on any platform or OS, extending massive PHP frameworks with C# modules, for instance. And then some funky exotic ones like crating games/apps/IoT software in PHP.
For most people (not saying it's your case) it's just a matter of not being that close minded and understanding that different companies or devs might have different language preferences. Or just to look outside their current box of thinking and see that any of the above might be useful for someone.