At the same time that I was working at an ISP on a product that would let employees from various companies connect via dial up and VPN into their corporate networks (whose gateways were also on our network) several of my co-workers were using a VPN of their own to connect to their home networks, but not to access the resources on those home networks (although some did that too). They wanted to use the internet from their machines at home in order to hide their internet activity from our IT department.
This is basically the same thing people do with VPNs now, only instead of hiding their internet activity from IT, they hide it from their ISP.
VPNs were always used for things other than connecting someone to a corporate network, it's just that most of the general internet population at that time (and I'm guessing you're old enough to remember this) were not aware of the technology and not tech savvy enough to set it up. This is true even for the employees of the companies we had as customers. We had to build entire software products that did nothing but hand hold people through setting up a dial up networking connection. It's not surprising that corporations were the majority users of VPN technology until the rest of the public (who don't have IT staff) caught up, at which point it became increasingly more common for people to use it to hide their internet traffic.