Sorry, the $50 properties are not selling at $50 because the lot is worth less than the cost of bulldozing the remnant of a house that is sitting on it.
I'm sorry; I didn't know we had somebody from the Wayne County Assessor's Office in this thread, here to illuminate our discussion with exactly how much these properties are worth.
Nobody knows what they are worth. They are worth more than $50. To somebody interested in a parcel of land in a major American city that serves as a cultural and potential economic hub for a metro area of 4 million people, they are potentially worth more than the $8,000 pittance it would take to bulldoze and clear the property.
The problem is the $2-3k/year property tax bill you're responsible for until the turnaround you're hoping for comes at which point you flip it, multiplied by the number of properties you're buying up to do this with. Nobody has any idea when it would happen, or even (this is critically important) if it would happen for these outlying neighborhoods
even if the city itself turns around. A revitalized Detroit will be more condensed and everyone agrees the critical question is, "what happens to everything between I-94 and 8 Mile?"