In social media, microtransactions like those usually account for an insignificant chunk of revenue compared to ads. People who have stores, run events spend a part of their marketing spend on reddit, and reddit displays ads for them until the money dries up. Reddit's ads have low conversion rate, so they are cheaper compared to better adtech. If they wanted to increase revenue, they would probably look to increase their datamining and user classification.
But profitability can usually be obtained by simply cutting costs. This means mostly layoffs (which I'm sure are coming) and to a lesser extent, cutting unprofitable features like the free api.