if matrix wants to have any remote grab at relevancy it has to drastically improve the experience of being on matrix.org, despite being a federated protocol.
take the example of mastodon.social:
+ good server, enough for most people's usecases
+ good uptime
+ federates well
matrix.org may be "good enough", but its uptime and poor federation make it a bad introduction to matrix as a platform.
There is no such payment structure.
Ask any of the matrix devs and they'll absolutely advice (and help you) to set up your own server.
The (stated) reason matrix.org is still the most prominent server is because there aren't yet enough well running public servers to have something like joinmastodon.org run well,
which is mainly because Synapse is very very badly programmed. Dendrite (by m.o) and Conduit (from the community) are starting to make very good progress now that the federation spec is stable.
Smol server part of the pixie.town infrastructure. Registration is approval-based, and will probably only accept people I know elsewhere or with good motivation.