(Fe)male conflict
Often we see some fruits (like citrus) with multi-locular, while some are with single (as in Jamun). Well, typically in a multilocular, all the seeds in individual locule were nourished uniformly, meaning all the produced ovules formed were "taken care" by the ovary (female). In Jamun, although there were many ovules, only the dominant ovule takes the lead, expands and destroys the other ovules, hence only one becomes the seed.
Let's see this from the perspective of survaival.