This is a completely specious argument. Of course there is no reason why we can't do a thing. We can do basically anything with computers. That does not mean that anything we do is a good idea.
People who don't understand how systems work often jump to decentralization as a solution to any problem. I'm not sure why. Maybe they've been burned in the past by a centralized service, and think the best solution is to remove what they perceived as their roadblock: the centralization.
Our current situation is nothing like traveling. You sit in your home, or in your car, or at your work, or in a park, or on an airplane, and you can access anything you want anywhere in the world, instantly. There's virtually no time between wanting to read your letter and receiving it. It's fast, it's easy, and it's uncomplicated. And you don't have to prove your identity if you've done it once in the past 30 days. Do you realize how that is possible? None of that is due to decentralized services. Every single service you use on the web is provided via centralized services. And they work beautifully.
Your wireless card listens for access point probes. It hears one from the AP it wants, and it connects. The AP begins the process of creating an encrypted connection. It checks that your credentials are valid, or passes the request up to a RADIUS server, that holds all the valid credentials of all the users. It then establishes the connection. Your host polls for a DHCP server asking for a lease, and the DHCP server, diligently making sure no leases have a conflict, gives you all the local network information you'll need. Your client sends a DNS request to the DNS server, which resolves, caches, and returns your request by polling the closest possible upstream DNS server, giving you a result that's geographically closest to you. Your browser initiates a connection, across your AP, across the cable modem, across the DSLAM, across the POP, across the MAN, across the many myriad routers, switches, traffic filters, interlinks, to finally get to the load balancers that maintain a balance of requests between the web servers of your destination. The HTTPS session is established after you verify the server is who they say they are, and then you tell the server who you are over HTTP, finally asking for your letter, and receiving it. And each route long the way has its gateway configured and routing tables filled with curated BGP tables so that they know exactly where to send your data to get you from a cable modem in Indiana to a datacenter in Brazil.
What would happen if we replaced every one of those centralized services with a decentralized model?
For one thing, you'd have less bandwidth and higher latency. All the devices on the internet would be constantly communicating, trying to find consensus, trying to update routes, trying to search distributed rings (my personal favorite topology) to find peers, connect services, authenticate trust relationships, query data, update indexes, etc. To say nothing of the potential for disruption of networks by various attacks or the difficulty of troubleshooting a random network failure in a massive decentralized network.
For another, storing data on your own host in your own home is taking 100 steps backward. As a very simple comparison, it's like taking your valuables out of a safe deposit box in an FDIC-insured bank and putting them on the front dash of your car. Even besides the security concerns, if you have a fire in your house, there goes your data! It's just a really dangerous idea to put data you care about in a place that's easily available to thieves and isn't backed up to an offsite location and maintained by professionals. That's what centralized services were meant to provide. It makes no sense to try and support those scenarios in a decentralized way, because the very idea of decentralized services is contrary to high-availability data.
Final thought: we put a man on the moon with centralized services. If we had done it using decentralized services, it would have taken a lot longer than it did with a lot more work, for exactly the same result. Sometimes it just makes more sense to be centralized.