My goodness, I see just the opposite: LOTS of synagaogues.
Like Henna saysa, it is just that churches are easier to spot festooned with towering spires and statues.
There's a very popular one near me near me near 94th and Lex, and an extrremely beautiful one down on Lex at 55th that does Wednesday tours. And another beautiful one near 75th and Lex (Temple Israel???)
They seem to gather around Lexington Ave.