Imagine someone in a LSA over Chicago who has a sudden problem. Where are they going to go? ORD? MDW? They're not going into Lake Michigan....
Now you've got a LSA at best glide of, say, 62 knots slowly trundling along under a declared emergency right into one of the busiest airport areas on the planet. Put yourself in ATCs office for a moment and ask yourself how you feel about that.
The pilot may feel safer at the higher altitude over the Bravo, but I would surmise (someone correct me if I'm wrong) that ATC (and the FAA by proxy) doesn't want that hazard in their Class-B airspace.
See the incident below - play it out with him dropping from above into ORD, JFK, or ATL. Listen to the pilot and how he responds, then think about whether or not he has a driver's license that would qualify him to fly SP without a medical cert.