I think that people beleive in cryptocurrencies as a concept, a new technology and the future of finances. And Bitcoin is leading cryptocurrency with biggest value and acceptance in real world and because of that people trust it the most. Although not very possible this might change in the future and ifopportunity some other coin takes Bitcoin's place, cryptocurrencies are here to stay and they could only develope further, they will not disappear.
To beleive in Bitcoin means to beleive in some totaly different economic approach but still the profit shouldn't be the most important.