I'd imagine the missing $8.5 million of profit goes towards the cost of services for ~10,000 new residents. That's only $850/year/person.

This study [1] should give you an idea: the median residential property operates at a net loss to the city at a revenue to expenditures ratio of 1:1.15 whereas commercial operates at a huge net gain at 1:0.27.

[1] http://landuse.uga.edu/Documents/cocsrep.pdf