VCs invest in bitcoins as they see a money making machine. It is a no brainer. VCs love to invest in hyped products and companies as their investment multiplies pretty quickly due to the hype.
Actually, good VCs like to build companies over the course of many years. Companies that continue to grow organically. Yes, there's often a "me too!" mentality in investing circles that can be hype-driven, but I think your statement unjustly belittles the diligence, intellect, and medium/long-term thinking that good VCs bring to the table.