I've discussed this question with my own oncology team (at a major research Cancer Centre), and they told me that when some prostate cancer cells evolve castrate resistance, many others continue to be castrate-sensitive, so it usually makes sense for someone with advanced prostate cancer to stay on ADT to slow the overall growth.

These days, we usually combine ADT with an ARSI (especially the one of the -lutamides), which will first delay the evolution of castrate resistance (sometimes by many years), and then slow down growth even in the cancer cells that have eventually evolved castrate resistance.