Question about request and response types inside context

[bkiac]

I have a question about the req and res objects in the context variable.
As far as I know, nexus uses an express server, so I expected to access an express.Request and express.Response inside context.
Is there a reason the types extend the HTTP.IncomingMessage and HTTP.ServerResponse respectively instead of their express counterparts?
Related types in /nexus/dist/runtime/schema/schema.d.ts

export interface Request extends HTTP.IncomingMessage {
    log: NexusLogger.Logger;
}
export interface Response extends HTTP.ServerResponse {
}
export declare type ContextAdderLens = {
    /**
     * Incoming HTTP request
     */
    req: Request;
    /**
     * Server response
     */
    res: Response;
};

nexus version: 0.26.1