You say that trustworthy centralized systems are obviously better simply because even today there is no viable alternative to them, but you can clearly see how that is cause for all types of problems. Most times you don't know who exactly you're trusting, and sometimes you are perfectly aware that those trustworthy individuals/companies are anything but that, but you're left no choice but to """trust""" them and hope they don't screw you over. And even if the company itself can be deemed trustworthy it doesn't mean that its individuals are too! This applies to all aspects of our lives, mainly because centralization up until now has been pretty much unavoidable due to technological constraints.
Enter the blockchain, smart contracts and all kind of buzzwords, and decentralization is finally starting to become a possibility. This blows wide open a whole lot of assumptions we make about our daily lives, so to avoid going into the political, economical, philosophical and moral aspects of what decentralization entails I'll stick to the one thing we know best: the internet.
The web as we know it today is pretty much FUBAR. You can see it on HN too, with plenty of news about websites screwing over their customers due to profit gouging, negligence, scaling/management issues... you name it. You have to trust these centralized websites that are completely closed off from everything else, and the website owner is completely in control of everything on its servers. You go to Google in order to do Google stuff the way that Google intends you to do and you have no choice on the matter. You liked that feature? Too bad, now it's gone because our internal tests found out that by removing it our conversion rate raised by 0.001%. And here, enjoy your new bloated, overdesigned UI. No, you can't switch to the old one. Also, your data is actually theirs', so they can just decide that they don't like you and just outright delete it, or sell it, or god knows what else. What do you mean you want to migrate somewhere else? Are you insane?? ...You get it. This applies to essentially every single website that you use, big and small. The data resides on the website's servers, whose security and management is up to the website's owner, and that's just how things work. In the worst case scenario websites could even act maliciously, as it happened when reddit's /u/spez abused its admin powers to change the content of comments that criticized him. All of this is unavoidable because of centralization, and hey, you agreed to the ToS after all.
That is not the case with Web3, because your data and your activity resides on the blockchain. Dapps access and interact with that data in a decentralized manner, and the resulting "status" of your account and the dapps themselves are the verifiable, unchangeable result of a sequence of actions that users performed on the blockchain through smart contracts. An example of what that means is that if for any reason a dapp you use decides to shut down their website for whatever reason, people would still be able to access and use that dapp by simply hosting the (usually open source) interface on another server and interact with the smart contract as per usual; the data and activity is still there on the blockchain, no one can seize or alter it and it will stay that way forever. You could also build your own website instead of using the official one. Also, dapps can use any other dapps' data with no restriction. To put this in perspective, the current web doesn't let you do that: you could use the provider's APIs, IF they're provided, but even then you would be subject to the limitations imposed, not to mention the provider has to actually stay up and let you access their APIs.
Granted, there is still some degree of trust involved as you could interact with a malicious smart contract, but it's still a _massive_ improvement over what we have now.
Another really cool aspect which makes it all worth it for me is the fact that you can use your account on any dapp without having to register to it with an arbitrary registration system you could be locked out of anytime: your account is just your wallet's keys, and you use those to sign your activity. Simple and effective.
Mind you, this is just the tip of the iceberg and something I wrote off the top of my head. There's a lot of cool stuff to be excited about that doesn't necessary involve money, but of course those take a lot more time and effort to be developed compared to marketing a get rich quick scheme, and certainly generate far less headlines.
We'll see how this pans out in a couple of years, but I'd certainly be gutted to see this die off because of human greed.