Positive feedback loops are present in everday life and usually referenced to something biologically based. Some biology based feedback loops include climate change, vomiting, and population growth. The positive feedback loop starts with a small change that self perpetuates into a snowball effect until the system reaches a new stable state.
The population growth of Splinterlands seems to be following a similiar feedback loop based around Hive. People spread the word about Splinterlands and get rewarded SPT. The rewards can be exchanged back into the game promoting itself. As more people join the game, the market grows and entices more people to participate. Eventually a plateau is reached on player growth and then becomes the new norm.
At a glance it seems like a ponzi scheme where the game relies on new players adding money into the game. This isn't the case though, because the game can thrive off existing members spending, playing, and socializing.
So far the development team seems to be able to maintain the game ecosystem stability with a expanding playerbase. Although, it seems the crazy amount of players joining certaintly can't be sustainable for years on end. Splinterlands will depend on keeping a core playerbase and not people looking to make a quick buck.