My goodness.
1. Scott Storch did not make the beat for "In Da Club." Mike Elizondo did it. However, he shares credit with Dr. Dre for the production. That way Dre maintains his status as a hitmaker, and Elizondo moves up in rank, owing Dre his career.
2. Bigdmakintrax is quite right. Eminem has a number of other producers, many of whom you have not heard of, and has co-writers on many different songs (if he gives them credit.) He, like Dre, is smart enough to see the lucrative business of involving himself in writing pools, or owning one. "Lose Yourself" is an example of collaboration to make a hit. He wants to extend his money making capabilities by establishing himself as a brand name producer, even if he "touches up" a beat here and there. In the end, he and the ghost writer make some money off the production. He is following Dre regarding that. He was apt enough to have Paul Rosenbourg start up Shady Records for him, and make it more than a lucrative boutique label. The cut from "Get Rich or Die Tryin'" is immense, especially since he did not put up the money for manufacture. He is a businessman and understands the rules of the game.
3. Going on what bigdmakintrax said, a big production company, with its own recording facility also hires professional musicians that, if stipulated in their contract, are exclusively used by the production company, and have to be on-call at all times. These people must carry their pager/cel-phone provided by the studio with them at all time, or have to answer at three in the morning to lay down a riff if Dr. Dre or whoever wants. They are quite handsomely paid with a steady salary. This represents a steady job for them, so they are inclined to do it. Thus, when all these people come together, a person that is guiding the project can simply play a simply melody on a piano, and then ask the string players, bass players, to come up with their own complements, or he/she will guide the live players to complement the original riff. Usually a bare track is used. In any case, there are session musicians that do this for a living that work for the production company for a salary or are hired to assist in a project, like an album. In either case, he can also have input from a panel of other ghost-producers that manipulate the song before or after. In either case, the name "Produced by Eminem" is more marketable for Eminem and all the parties involved than "Produced by No-Name." If they can establish a steady stream of calls for production, all these people, from session-musicians on up through the production outfit and all the way to Eminem and his agent and manager- make money off this. The people doing this know what is going on, and they want a steady stream of income.
4. Irregardless of who he exploits for production, the bottom line is that he is making money and entrenching himself as a production entity to be dealt with. That touches on point #3.
5. He is trying to get as much money as he can using his name. He's also being advised to do so. Wouldn't you, if you were in his position? Think about it.
Sincerely,
God
