True, times change. When I built a PC myself for the first time around 15 years ago the "standard" cases were designed with one intake fan and one or two outtake fans. Usually resulting in negative pressure inside the case. (Not even talking about cases 20 and more years ago which didn't even have any fans and the only outtake was through the PSU). So no wonder they were dusty as heck back then. Over the last decade things changed. And now you can easily create positive pressure inside the case and combined with a dust filter it almost eliminates the problem.
True, times change. When I built a PC myself for the first time around 15 years ago the "standard" cases were designed with one intake fan and one or two outtake fans. Usually resulting in negative pressure inside the case. (Not even talking about cases 20 and more years ago which didn't even have any fans and the only outtake was through the PSU). So no wonder they were dusty as heck back then. Over the last decade things changed. And now you can easily create positive pressure inside the case and combined with a dust filter it almost eliminates the problem.