If bitcoin is not really secure, then how come it is still existing and dominating until today?
Blockchain technology is secure and about your question. It is because of the investors, the market cap, that makes the value of bitcoin high and low. It's the blood line of bitcoin from the money of the investors so it is still dominating until now.
Its market capitalization proves it that people are trusting on bitcoin because it's secure.
Yes.
No investors will risk it's money to a thing that he doubts to lose his money.
There are investors that loves risk even he don't know what he's investing.