The way I read it it was referring to the type of businesses that arise in already dying residential areas, due to the rent being cheap, etc. and individuals can start their yoga studio or karate doja and such. The businesses themselves aren't bad, but they are a symptom of a neighborhood in decline. Don't know if that is true, but that's how I understood it.
Also, these businesses don't need walls or public restrooms. If the floor is concrete, CVT, carpet, or whatever they still just roll out some padded mats. No one cares what the ceiling looks like or if the heat works. No remodeling required to get their tenancy started, and none required to replace them with a more lucrative business. Landlords are not afraid to sign up such tenants even if the rent they'll pay is low. A tenant like a dentist or coffee shop requires more complicated improvements, will be charged higher rent, and will signify that the strip mall in question is not dying.
The stoa was the ancient greek strip mall, and I suppose doing philosophy involves little to no remodelling. I can imagine the early stoics putting up resiliently with the misfortune of being moved on from each venue every time a better-paying tenant came along...
Haha that's a funny image. I can't imagine that freelance philosophy pays much better now, so from now on I'll consider a professional philosopher to be another "death tenant"...