People (by which I mean average computer users) didn't "start ignoring security", they never bothered to unignore it in the first place. Early Windows editions didn't even ship with a firewall at all, people were rawdogging the internet out of the box without ever stopping to consider the consequences.
... because people (by which I mean software vendors who should have known better) irresponsibly failed to create secure systems for those average users to use. A whole lot of which came to be justified by "it'll be behind a firewall" thinking.
I remember in the Windows 95/98 days asking my friend for his IP address and then browsing through my windows explorer to his mum's fully shared windows C drive. She had her computer plugged directly into the modem and was using ICS to share the net to my friends computer.
I sent them a screenshot of her shared drive through ICQ, and not long after she bought a router.