I think you have your body to thank for that. All my jeans get completely destroyed at the crotch within a year. I just think that different body types create different movements and wear.
Crotch bursting (which is the hilarious technical term for it) is more common than you'd expect. Major reasons are over-washing, but a bad fit, stretch fabric, too-thin fabric, and poor stitching are the major reasons for failure.
If you are finding that your jeans are always bursting at the crotch, identify first if it's happening at a seam. If so, buy a different brand. If it's not, wash your jeans less.
If you must wash them, do it inside out, and always let them air dry. Don't use bleach, or any detergent with oxidizing chemicals (this is more common than you'd think). Ideally you should't even wash them in a machine. I think the absurd movement to wear jeans for months without washing is unacceptable if you ever plan to wear them outside of sitting down at a coffee shop, but hand washing them is much gentler and will have your jeans last for years. I own more than one pair of jeans that are years old, and have seen hundreds of days of use without any damage.
