when using middleware, you have broad ability to capture the request and do something about the request at certain layer as well as respond that will be sent to browser/any client, whether it has something to do about how user authenticated, format the input from user, modify response, etc

using middleware also give you capability to apply certain condition to all request(as global middleware) or only applied to certain route (routeMiddleware).

meanwhile with Policy/Gate, it is more focus on how you control user for accessing certain resource (could be a model or simply access to view).

one last thing again, add a middleware means you add a logic that will be executed in Pipe/Stack along with other middleware (the one that Laravel provides, and other middleware that you created) and that is not necessary true for Policy/Gate. Hope it helps.

Automatic Policy Discovery