This is what happens when you have a sub par public school system. It is not as easy as just signing up at the neighborhood school, the "good" elementary schools are way overcrowded. In fact, there was a 90 kid waiting list for K seats in 2 Greenwich Village schools last year. With private school tuition over 30k a year in many cases it's easy to see how parents can become invested in getting their child into a G&T program. Especially condidering that only 1/3 of those scoring in the 99th percentile on the OLSAT even get a seat in a citywide G&T school.
That said, test prep will only exacerbate the situation and more and more truly gifted kids will be shut out of programs that would benefit them the most. My daughter (on her own) did very well on her first test but that is far from a guarantee of her getting a seat in a public gifted program. It's quite discouraging.