Driver retention

Looking for some insight here as I am at a loss. We are a 12 truck operation based out of western Nebraska. Constantly struggling with keeping drivers around long term. I feel we pay damn well 25% of gross and a weeks paid vacation annually and end of year performance bonus. Run primarily 379’s that are well taken care of and 4 year old to new timpte hoppers. We have two dedicated contracts have had them a long time as our bread and butter and fill in the gaps with grain and feed stuffs to get from A-B. In all we run close to 90% loaded miles in a round trip of our lane. If you break down the lane by miles the driver makes on average .65-70 cpm a week. Annually on a steady driving operator is doing well over 100k and home nearly every weekend and home a night or two during week if they live here in our area. On average there guys do 3000-3500 miles a week almost all the miles run east to west on 80 Utah to Iowa which is really quite easy running the big road most of the miles. So what the hell gives?? Has the culture changed so much in the workforce that people just constantly want to jump ship?? I’m not an overbearing boss I’m pretty dang easy going unless you are not maintaining your schedule then I will lean on you at that point. Everyone is paid bi weekly just like all my other employees no bs the check is always there and I try to do my best to accommodate concerns or issues right away when they arise. But I tell ya in the last couple years I’ve had just one out of several quit respectfully and give notice the rest I come back finding a truck parked and cleaned out with no notice no excuses no nothing. I’m sorry no pun intended but out here a 100k plus job is pretty d*** good money and checking around I’m payin a top wage. If I doin something wrong point it out to me cause I’m at a loss. Tires of there being no loyalty or pride amongst drivers anymore I’m old school.