The cost of those to the service provider is generally not zero though. And cost is per user, and these all have fewer users than mainstream social media and “services”.
Though Linux is an exception here, with it costing only the time of hobbyists (at least as far as I know)
It gets more complicated when you have to factor in profit…and then shareholders…and then demands for exponential growth. That makes it harder to estimate how much is costs, how much is greed.
(Not that all of this should be free or delivered at cost, necessarily – it’s healthy for people to be able to make a living off of products or services they provide)