I've noted during the last few (about 10 to 15) years, many manufacturers are now skimping on underbody finishing with almost no use of coatings, underseal/sealants these days. The cars just get left in the (now less effective, but environmentally better!) factory primer dip and modern galvanised metal means they are extremely unlikely to rot out during the warranty period, so they just cheap out and save the money. It doesn't bode well for longevity beyond warranty though and it'll be interesting to see how long these cars last in old age.
My brother had until recently a 30 year old Audi 100 in it's original paint, the underbody was entirely covered in polyurethane underseal about 3mm thick. All cavities were heavily flooded with cavity wax, so much so that it still oozed out the drain holes in hot summers, even after decades! It was also an early galvanised car & I think at the time the zinc used was some microns thicker than current. It had also been dipped in the nasty hot phospate primer, used at the time to negate the fact most sheet steel used in car making wasn't yet galvanised. (this was rich in heavy metals & terrible environmentally!) This left a layer about 10x thicker than todays thin film zirconium cold dipping that new cars get. It was virtually perfect underneath even after 100k+ miles when he sold it on, and he doesn't look after, or clean his cars properly underneath as I do either!
He now drives (he's a tight git!) a 1999 Skoda fabia, it's also finished as the above Audi was and is utterly free of any underbody corrosion at going on 140k miles.
Compare that to my last MG, a Mk1 ZSEV that had more underbody rust setting in underneath around the seams when I sold it at less than 18 months old with 16k miles! (top of the car was perfect and looked brand new though!)