Honestly, most new games just fucking suck. They're too expensive, often don't run properly at launch even on excellent hardware, and those that don't have micro-transactions built-in require you to purchase DLC to get the whole game.
On the other hand, the older titles almost always run well on my machine, have a ton of community DLC, and in general are just designed better because they were built to bring the player as much fun as possible, not to extract as much money as possible.
Plus, the quality content generated from 2005 - 2015 represents some of the best ever, and can provide hundreds of hours of enjoyment before you even get into the 2010s. Why waste money on something that may not work, and that I likely won't enjoy as much as the games I bought 10 years ago?
It's why I usually wait at least a year after release to consider whether or not I'm going to buy a title.