Probably because you LIVE IN NEW YORK CITY!!! I visited NYC about a year ago and felt like I saw the most bizarre thing I had ever seen in my life thus far every five minutes...
But since you insist on letting it shock you...my gut reaction says some kind of African altar.
I know that many traditional African religions involve building altars such as the one you describe. I also know that many of these religions integrated Catholic elements into their rituals after European colonizers, uh, lets say paid them friendly visits, which would explain the inclusion of the saint statue in the altar.
Although Santeria, as Rhias Hall, pointed out, is a likely possibility, it could also be an altar a number of other lesser known tradional religon which sometimes just get lumped together as Santeria by the media. I know that there has been a strong African influence on the culture of the Dominican Republic.
If you think that this is what it is and you really wanted to get to the bottom of it, you should check out "Flash of the Spirit" by Robert Farris Thompson. It is a book that catalogs the rituals and artwork of countless religious groups past and present in Africa, including if I remember correctly Santeria.