Why do you think...

There would be many reasons.
The big one though would be making sure it was quicker. They weren't to know how long being burned alive by a big fire would take, how much it would hurt. To many of them suicide was the option of making it quick and easy.
Could you imagine waiting weeks, or even hours, waiting for the end to come? Or just standing there watching as a wall of fire approached? Ugh, the whole scenario gives me nightmares.

Tough to really say. Like mentioned, being charbroiled alive would be a painful way to go, but I do not think I could do myself in. I would likely binge on whatever I could get my hands on and hopefully be passed out cold when the flame waves came crashing in... hmm... so, yes, I suppose I would end myself earlier by the sounds of it.

These catastrophe films are very profound because all of us will face our final hours as in having time cards clocked out sooner or later whilst others get taken out quicker. It is all a crapshoot. I suppose everyone of us realizes the end is coming, but 'when' is really up to luck itself. And, so many of us feel almost immortal and wastes a lot of quality time doing sweet F A. When I get old, I am surely going to regret typing these posts out whilst I could have been outdoors enjoying nature or even visiting forgotten friends, but by then, I would have forgotten how tired I was after a hard day's work which was exasperated by staying up too late watching films and posting on boards. Ah, damned if we do and damned if we don't. 

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Say, that's a nice bike...