Is there a specific reason old public works projects used to be a lot more elaborate aesthetically versus the "lowest bidder" approach they take today?
The second reason is that public projects have a real problem trying to control labor costs during projects. The most artistic and aesthetically pleasing works of craftsman ship taking time and money public projects can't support right now.
In NY, every minute you allow an employee near a ladder costs you money due to Workers Compensation costs.
The Power Broker would be my recommended reading.
In any case, a lot of the subway art described here was from before the '30s -- many of the stations described are part of the original IRT line, which opened 1904.
Rehabilitating the subway is not a new, grand project. It also would‘ve primarily benefitted the poor people in a way contrary to his visions. Finally, it would‘ve competed for federal money with his precious highway projects since the federal government would be reluctant to allocate too much money to one region. So the subway had all the things going against it, in Moses‘ opinion.