VPNs don't pose an obstacle to monitoring any specific activity, and as many VPN-using criminals have found, even their ability to stop law enforcement from identifying you is limited. So they've been less of an issue. Having said that, I would note that Mullavad was forced to remove port forwarding in response to law enforcement interest, and I don't think it would be too surprising (or too dystopian) if in the future "connection laundering" is a crime just like money laundering.