In bitcoin, you don't even have promises. All you have is faith that some anonymous people will trade things that you can live off of for your bitcoin.
Maybe some people don't want to be part of a fraudulent, built-to-corrupt system where their money is inflated as there's demand for new loans. Maybe some people just want to use something that leaves room for questioning; that its usage is not forced to satisfy ones' interests; that provides free speech and freedom of choice.
There's a difference between trusting a system and having faith to a system: No one forces you the latter. You ought to respect those people who have different political beliefs than you. No?
So, you would rather trade your car, house and bike to anonymous people for a number. And then have faith that in five years other anonymous people will voluntarily give you the equivalence of your things? You would rather do that, than to have a guarantee in the capital of the banks, the loan contacts/collaterals of the borrowers and legal enforceability that the equivalence of your things will be returned? All that because some people in the banking system are corrupted? And because borrowers are "forced" to return you the equivalence of your things?
Although this is a highly simplified description, you are basically right. This is exactly what all Bitcoin investors have been doing for years. Just as with the Wal-Marts and Macy's of the 1980s and 1990s, people are realizing they can get huge returns by investing in penny stocks (yes, even the internet one) and hoping to strike it rich. Unfortunately, while the Wal-Marts of the 1980s and 1990s had sensible rules around securities and protecting investors, those rules are totally absent in the cryptocurrency industry. It is completely unregulated, and the only way to prove that you have been in compliance is to use the coin's blockchain. So even though many penny stocks were fraudulent or otherwise had other problems, investors could use the SEC to settle disputes and do their due diligence. Cryptocurrencies have no such tools and no such oversight.
But that doesn't mean that every cryptocurrency is a scam or that all are a scam. Like penny stocks, not every blockchain project is a bubble that is destined to pop. There are legitimate ICOs out there and legitimate blockchain projects. The technology that runs Bitcoin and Ethereum is enormously promising. The financial benefits to using a blockchain technology to secure transactions are, in my opinion, clear. For example, Bitcoin's great strength is that it is widely used and accepted worldwide as a means of payment, and is highly protected by a large number of miners, which makes it much harder to hack or double spend. I think people will continue to invest in legitimate technology projects and blockchain projects that have real utility. Just as people continue to invest in the stock market and expect good returns, I think investors will continue to buy into cryptocurrencies.