I heard from a friend that has a Hyundai that it is difficult to jump start them.
She said the guy had to use two battery packs, one the normal handheld one, and another that was much larger.
Why is it hard to start them?
I'd suggest your question is subjective. I've owned several Hyundai vehicles and have never had that issue. And yes, I've needed to get them jumped before. My current vehicle, an '08 Azera Limited, had the battery become dead. Connected my truck to it via jumpers and it fired right up.
There may be something else going on with your friend's car or the battery pack which was used may have been weak. Could be any of a number of reasons why, but there's no evidence Hyundais in general are hard to jump start.