In all applications of digital direct to fabric printing, a fixation process is required for durability. In the case of sublimation, the dyes need to be sublimated (vaporized and then deposited) into the fibers of the polyester textile. For pigmented inks, the pigments need to be "bound" or fixed to the fibers.
If this final process is not completed, then the color will be easy to remove from the textile.
Finally, for dye sublimation and direct to fabric sublimation, the dyes are bound to dispersants. This is the reason why prints before fixation look so dull; you are seeing the color of the dyes through the color of the dispersants. Heating dye sublimation inks is always necessary to see the true color of the ink.