Two reasons:
1. Organ donations. There is enormous pressure coming from doctors, hospitals, and other interest groups who stand to gain prestige and $$$ in the hugely profitable body part transplant industry.
2. A debased culture that no longer values life. Scratch a euthanasiast and you will find a "pro-choicer" underneath.
Of course, not thinking that way, I didn't think of that. It appalls me that people are so interested in money that all they can think of a dying person in terms of is what they can harvest from them to make money and how fast they can do it; not even waiting till the body's cold. It's morbid and inhuman.
The devaluing of life is evident in other areas, often in subtle ways. When there is a car accident during rush hour, what does everybody think? "I hope nobody was badly hurt, or killed." If that's what everybody's thinking, why do the tv and radio reports focus on the effect it will have on commuters, and never mention what anyone who cares about life is worried about? Children are beaten to death by their parents every day, and usually nobody cares. Unless there's something else about the case they think is important. Like a celebrity, or a mystery with lots of twists and turns. There's been a rash of homeless people being beaten to death, and most people won't even hear about it. Most of those that do hear about it, won't pay any attention. I can't drive for 15 minutes without seeing at least one driver who completely disregards every life on the road in his quest to win the race. If an animal runs into traffic, many drivers are more apt to aim for it than try to avoid it. Most people don't bother pulling over for emergency vehicles anymore. They don't want to be slowed down, just to save some stranger's life. We shouldn't be surprised that people want inconvenient people to just stop existing, as though it has nothing to do with life and death.