Used four-wheeler trucks are usually more affordable than new trucks and may be easier to work on without hiring a mechanic. The lack of sensitive gauges and other high-tech features can also be beneficial for off-roading purposes.
Well-maintained older vehicles are usually still reliable enough for most uses. They typically require more ongoing maintenance than a new truck, but the monthly cost is still generally less expensive than a new car payment. Some people may also feel more comfortable driving through rough terrain with an older truck, because there is less financial investment if something goes wrong.
Older 4x4s are also usually easier to work on without advanced mechanical training and equipment. The more simplistic engine design and lack of computer controls makes replacing most parts easier. The low-tech design can also help make offroading modifications easier. For example, automatic tire pressure gauges can become inaccurate if larger tires are installed or if the tires are deliberately under-inflated. Modifying older trucks also avoids the potential pitfalls of voiding the manufacturer's warranty, which is generally expired anyway. However, certified preowned trucks bought from a dealer may come with a renewed warranty.
Many people also love the style of older trucks. Older 4x4s have a distinctive square body shape, while new trucks tend to be more contoured and aerodynamic.