I kind of mentioned it already, but apart from payments or other transfer of digital ownership, there shouldn't be much need for on-chain transactions. In some years when, hopefully, L2 technologies have matured and grown to live up to their promise, those won't have to either (there is always the initial on-boarding of course, but credit cards and mobile payments have those too)

As for "who's going to run the nodes", if cryptoeconomics or users don't take care of it, I assume businesses will. The nice thing is that regardless, the payment for this infrastructure is also facilitated through cryptocurrency transactions on L2 networks. For someone who doesn't want or need to take ownership of that, it can just be proxied through to the client and not need to be the concern of the developer of publisher of the app.

Of course businesses can still choose to pony up for it proactively of they have the finances to support it, potentially running it themselves or through a third party. You can always fall back to "the old ways" for certain things when it makes sense.