It is typical for investors to not sign NDAs. There are plenty of resources on the web on why this is the case (see below). As we want to make sure we can expedite your fundraise from us, we don’t sign NDAs.

feld.com/archives/2006/02/why-most-vcs-dont-sign-ndas.html

forbes.com/sites/wilschroter/2013/08/22/why-investors-dont-sign-ndas/