A lot of this isn't because they are inherently bad cars, but because parts/service support is lacking. They were a good value when new, but there was no intention of them being in service 15+ years later, even if they were capable of it with a good supply of replacement parts.
Getting parts for an older Hyundai or Kia is often difficult. Some stuff we still stock like Sorento u-joints (at $105 or so each) and coolant reservoirs, but on the early "luxury" cars, forget it. Aftermarket support for Hyundai/Kia is even worse than OE, which compounds the problem.
What's really going to bite Hyundai/Kia is their inability to supply collision parts for very new cars. It really upsets people when they buy a new car, it gets wrecked in a few months, and the parts to repair it are on backorder with no ETA. Yet, there are new cars on the dealer lot. You can't explain it to customers, and if Hyundai/Kia keeps it up, they are going to hurt the reputation they are trying to build. Having a nearly new car out of service for months due to a lack of parts is not good for building customer loyalty and trust in the brand.