Helium is very much centralised because it has to (by the nature of their offering) lock down the end-user devices heavily. They have a single approved manufacturer last I checked.
It essentially operates as a unregistered and unregulated ISP and that isn’t something to be taken lightly. It does that by pushing all legal and regulatory liability to operators. There’s also a lot of scams with operators faking their signal etc.
Running a node also likely violates your ISPs ToS - can you contractually resell bandwidth?, so it has similar concerns as what AirBnB etc for the housing market.
There’s nothing stopping something large ISPs from blocking Helium traffic and/or suspending customers for running a node. Alternatively, if this gets big enough, you’ll see ISPs offer LORA hotspots of their own.
Ultimately, it is a very much VC-funded company running regulatory arbitrage on a global scale by using crypto instead. It’s the same if Uber decided to pay drivers in UberBucks a decade ago - that doesn’t change the offering, it just makes it easier to scale while pushing off any regulatory liabilities (including taxation).