The area has some low zoning in general. Riverdale/North Riverdale. Unfortunately developers have to cater to it or file a petition to rezone "X" parcel or block.
Some maps:
1)
https://www1.nyc.gov/assets/planning...maps/map1b.pdf
2)
https://www1.nyc.gov/assets/planning...maps/map1c.pdf
Now if you compare to the South Bronx, big difference:
3)
https://www1.nyc.gov/assets/planning...maps/map6a.pdf
A lot more density can rise.