Big tech companies tend to re-invest something upwards of 80% of their profits back into R&D in order to maintain a competitive advantage. You certainly don't hear of giants like Samsung, AMD and Intel looking for seed capital to fund their next advancement in technology, they learned long ago to put their profits back into themselves in order to grow in size and capability as time goes on.

If you build something successful and manage it all correctly it should easily cover it's own development costs for future iterations of it. For small time devs like you or I we work without a decent amount of income but do it because we see the capability to build something that will produce capital.