How can people actually enjoy adrenaline rush of riding a roller coaster, sky diving, or bungee jumping?

Like with some things, extreme sports are an 'aquired taste' & you either like them or you don't. Even if a person likes jumping off bridges or out of planes they're still scared, they just like the adrenaline rush that their instinctive fear gives them so they keep doing it.

Scares the sh...HECK out of ME, but I can understand the attraction.

I can't speak for sky diving or bungee jumping, but when we're on amusement park rides, it's one of the few times in our lives when we're actually living.

We're not "past-ing" or "future-ing"
we're fully in the present.

It's an addiction. Some of us are born with what they call a "risk-taking gene." It makes us prone to take greater risks than most people. I have about 1,000 military parachute jumps to my credit, even though it scared the crap outta me everytime I jumped. I forced myself out the door because the feeling of exhiliration is all but overwhelmind! : ))

Some people's body generates a chemical called endorphin.
According to wikipedia, the term endorphin rush has been adopted in popular speech to refer to feelings of exhilaration brought on by pain, danger, or other forms of stress, due to the influence of endorphins. When a nerve impulse reaches the spinal cord, endorphins are released which prevent nerve cells from releasing more pain signals allowing humans to feel a sense of power and control over themselves that allows them to persist with activity for an extended time.

If your body does not produce as much of this chemical, it is not as enjoyable to you as it is to the person who has a large production of it. I am in the former category, and consider myself to one of the more laid-back type of people.

How can one not, would be my question. However, I do realize that it's all up to the personality. I want a little adrenaline in my life, but I do want to be safe.

Because its such a good feeling. Undescribeable

I wouldn't do any of those! I will stick to something that feels secure - aerobatics (stunt flying).