Christian Zionists are a very import part of the Israel lobby and extend the power of that lobby in many places that it otherwise wouldn't be. Given how many left leaning Jewish people in the US have decreased their support for Israel, Christian Zionists give them a real ground support to the movement that is otherwise more dominated educated elites.

And depending on your definition of 'Zeal' the christian zionists often have more. A educated Neo-Conservative might be a strong Zionist but not will not come across as having Zeal, while a Baptist Christian Zionists might come of as pure Zeal.