YSK: While you're on Lemmy/Kbin/Fediverse, you're not "the product" but you're also not "the customer".
Why YSK: Getting along in a new social environment is easier if you understand the role you've been invited into.
It has been said that "if you're not paying for the service, you're not the customer, you're the product."
It has also been said that "the customer is always right".
Right here and now, you're neither the customer nor the product.
You're a person interacting with a website, alongside a lot of other people.
You're using a service that you aren't being charged for; but that service isn't part of a scheme to profit off of your creativity or interests, either. Rather, you're participating in a social activity, hosted by a group of awesome people.
You've probably interacted with other nonprofit Internet services in the past. Wikipedia is a standard example: it's one of the most popular websites in the world, but it's not operated for profit: the servers are paid-for by a US nonprofit corporation that takes donations, and almost all of the actual work is volunteer. You might have noticed that Wikipedia consistently puts out high-quality information about all sorts of things. It has community drama and disputes, but those problems don't imperil the service itself.
The folks who run public Lemmy instances have invited us to use their stuff. They're not business people trying to make a profit off of your activity, but they're also not business people trying to sell you a thing. This is, so far, a volunteer effort: lots of people pulling together to make this thing happen.
Treat them well. Treat the service well. Do awesome things.
Lets see what the future brings. As long as the user count is low there isn't much of a problem, but if instances suddenly have millions of users, it will get expensive for admins to run the service. If too few people donate (what is usually the case), admins are forced to search for other ways to finance the infrastructure.
The other point is AI, wheter you like it or not, if Lemmy is big enough, the content (conversations etc.) will be used to train LLMs. Also, the content will certainly be interesting for advertisers to learn user preferences.
The difficulty comes with scale.
So, in theory, of we keep the individual instances manageably small and spread everyone across multiple instances we should be sustainable. As it generally doesn't matter which instance you're on so long as its federated with the community at-large we could keep the instance servers affordable for the admins and users that are able to financially contribute.