Fashion Design major here, with a key focus on materials science...

Stretchy materials are inherently weaker, and their integration with any other non-stretchy material will diminish the lifespan of the garment made from that textile. Especially at the seams.

Elastics are broken down by UV (sunlight), hot water, detergents, fabric softeners, dryer sheets, intense heat (dryers), and use. So if you wear stretchy jeans outdoors on a regular basis, and wash them in a washing machine regularly, they won't last long.

But people wash their jeans FAR too often.

Once a year, or so, is all they actually need. No, seriously.

The founder of the Tobacco Motorwear company just posted a video to his Instagram last week, where he talks about how actual selvedge jeans are made, cared for, etc. The pair he is wearing in the video he's had for 10 years, and has washed 3 times.

Our knee-jerk reaction (carefully cultivated by the personal care products industry) is Disgusting! But, in reality, it isn't.

We wash EVERYTHING - clothes, hair, faces - far too often for our good, and 99% of those resources are wasted... the material, the clothing item, the detergents, the water, processing the detergents back OUT of the water at the wastewater treatment plant, etc.

So yeah... stretchy jeans won't last long. But they'll last longer if you don't fall victim to the manufactured myths promoted by people who want to sell you cleaning products and appliances.