Indenture ended because it stopped being economically worthwhile for Britain

Evidence

Simply put, the indenture system was not worth the argument. From the time the British indenture system was abolished until the Second World War began, the international labor market shifted to other patterns of migration in which state management was less formal. The global economic downturn of the interwar period brought less demand for laborers across borders, but it also marked a new era of experimentation with transnational workers from the Indian subcontinent, particularly in Africa and the Middle East. By the end of the 1940s, the rebuilding of the global economy and the rapid industrialization of several regions of the world required the large supplies of transnational labor that subsequently emerged as the standard solution to crisis in the world economy. Through this period of shifting structures of labor recruiting, a clear pattern of postcolonial labor diaspora began to emerge that would send workers from South Asia across the globe. — Junaid Rana, Terrifying Muslims, 490