You own a very valuable thing and you want to go to holiday without it, but there is nobody who you trust and who can look after the thing. So you take somebody unknown to guard it. You pay him a fee hoping he doesn't run away with the valuable think. How much would you pay?
I think you should pay for the fee minimum the value of the valuable thing!
But now to bitcoin. Do the story again: You own a very valuable coin which is guarded by somebody unknown (the miners). You pay him a fee (mining profit) that is much less than the value of the coin (market cap of bitcoin). Why don't the miners hold short positions on the coin, bring value of the coin down with a large majority attack which destroys any trust in the coin and go with benefit from the destruction?
I asked this fundamental question about bitcoin in a stricter way 2 days before in this question and similar in this question and there is also a bounty for an answer, but there is only less interest and no upvotes and no good answers. I think the question is fundamental, and so I tried to do it in an easy analogy now.