one of my least favorite things about taking VC money is when they have some audit firm email you to confirm that they own the stock. it's so annoying and they email you 25 times until you respond. if i ran a VC firm i would simply not put my founders through this suffering

As an ex-auditor a long time ago, the firms don’t have a choice. 

It’s an audit procedure which is required for the firms to validate the non-publicly listed holdings that eventually goes into a line item in the audit report so that the shareholders of those firms know that the management has not misused funds.