Because of what's happening in [government, media, science, public spaces, labor markets]. I view all of them as examples of the same underlying phenomena.

In government, you have the UK voting to remove itself from the EU, and then when the referendum passed, the prime minister resigning, all of the major proponents of the referendum resigning, and Scotland threatening to secede from the UK (again). You have a U.S. president who starts his term with under 50% approval rates, the lowest since WW2 [1], to cries of "not my president", and Congressional approval ratings below 20%. You've got continued polarization - instead of converging on compromise candidates in the center, the Republicans has moved rightwards toward nominating actual Nazis (5 running in 2018) [2], and the Democrats have moved leftwards toward nominating actual socialists [3].

In the media, you've got an Overton Window that doesn't overlap - no matter where you are on the spectrum, there are publications with a large readership who are publishing what you perceive to be blatant falsehoods. Take a look at the comment sections of the same story on Breitbart [4] and News & Guts [5]. Could you imagine a reader of one reading the other with any sort of any open mind? Would you consider anything you read there an example of trust?

In science, you have movements such as anti-vaxxers who would reject one of the most important health advances of the last century because they don't trust it. You have continued rejection of climate science, largely because it's inconvenient. You have a replication crisis in many social scientists.

In public spaces - go to an airport and listen to the loudspeaker say "Please report any unattended baggage or suspicious persons to the nearest TSA agent" and think about what that's saying about the level of trust in society and the constant messages of fear. There was another recent story on HN about air marshals secretly tailing random civilians [6]; that's not exactly something that happens in a society that trusts its citizens. There's also continuing helicopter parenting [7] and the assumption that everything around you is dangerous, which tends to become a self-fulfilling prophecy.

And in labor markets - I did a bunch of market research on a startup to fix unemployment a couple years ago. My hypothesis was that with all the startups desperate for workers, and workers desperate for jobs, it was a simple information problem to match up supply to demand and make everything efficient. What I found was that hiring isn't really an information problem, it's a trust problem - employers are terrified of getting a bad hire and so reject a lot of candidates that with a little training could be great employees, and similarly employees are terrified of ending up in a career dead-end and so are unwilling to invest in significant self-study or commit to a career path or potential employer. End result - unemployment and underemployment even though there are both workers and jobs available.

All of these are pretty far afield from cryptocurrencies, but you asked why I believe the #1 problem in the world is lack of trust, and that's why. A world where people trust each other is one where they're willing to take risks on the assumption that they won't be taken advantage of, and that is...very far from the state of the world right now.

[1] https://projects.fivethirtyeight.com/trump-approval-ratings/

[2] https://www.vox.com/2018/7/9/17525860/nazis-russell-walker-a...

[3] http://www.cc.com/video-clips/jzbxb9/the-daily-show-with-tre...

[4] https://www.breitbart.com/big-government/2018/07/29/trump-wa...

[5] https://www.newsandguts.com/trump-will-shut-government-doesn...

[6] https://news.ycombinator.com/item?id=17635761

[7] http://www.dailymail.co.uk/news/article-462091/How-children-...