"Why?"
1. Rising indebtedness, both private and public, and concentrated asset ownership. Debtors have an incentive to favor money creation and inflation because it reduces the value of their debt in real terms; creditors have an incentive to favor the opposite. When a small number of creditors hold the loans of a large number of debtors, or when the government itself is a major debtor, there are significant democratic pressures toward monetizing the debt. (Berkshire Hathaway annual reports talked extensively about this in the late 90s and early 2000s and still sometimes do, though Buffett believes this will happen through gradual inflation rather than a crisis.) We've already seen some of this with the political pressures on Janet Yellen and Jerome Powell this tightening cycle.
2. A large injection of money through QE that has so far stayed in capital markets and not made its way to every-day transactions. One of the great mysteries of the 2010s is why the large increase in the money supply did not cause inflation. My explanation for that is that it did - but only in asset markets, like stocks, unicorn startups, CA real estate, Bitcoin, etc, because that is what the people who had money chose to buy with it. This is viewed as wealth inequality rather than inflation. If you fix the wealth inequality - either by government redistribution or by rich people finally choosing to consume rather than invest - you will get the inflation, and may get it very rapidly.
3. Historical perspective: once inflation pressures start, they are very difficult to control, and usually result in a feedback cycle where expectations of future inflation cause people to get rid of their cash more quickly, which makes the velocity of money rise, which makes inflation even worse.
4. General loss of trust in institutions, particularly the financial industry, the government, and the Federal Reserve. Obama's actions in 2009 basically saved us from a total financial meltdown. It did so at the cost of trust - there's now a widespread (and not entirely unjustified) belief that the system is rigged against the common person, because when they make dumb financial decisions they're on the hook for it but when Wall Street makes dumb financial decisions the government bails them out.
5. Greater information awareness - thanks to the Internet - and also the rise of filter bubbles, again thanks to the Internet. The former exacerbates the loss of trust in institutions. The latter allows people who have lost trust in existing institutions to start forming their own, and to recruit other people towards their point of view. Together, they create competition where hegemony previously reigned.
6. The rise of potential technological alternatives. Bitcoin sucks as a currency - it takes 11 minutes to confirm a transaction, the UI is bad, fraudsters and scammers abound, and the network is limited to ~7 TPS. However, all of the elements of a functioning currency are there. People do trust it to maintain its value - 10 years in and people have lost individual Bitcoins through failing to secure their private key or entrusting them to the wrong exchange, but the network itself has never been compromised or rewritten. It's possible (though clunky) to transfer value with it. It's possible to maintain stable identities and records of ownership. Efficiency and ease-of-use can be fixed, and the fundamentals are there.
7. The potential need, in the near future, for computers to act as economic agents on their own behalf without human intervention. Services like Ethereum, Iota, Golem, and Filecoin are fascinating here. It may be that cryptocurrencies end up being foremost for machines to transact in and only incidentally for humans.