"So, if T is bad, why was it six years before my PCa returned?"

OK, let's try this.

Think of testosterone as kerosene and prostate cancer cells as little sparks. If there's a big puddle of kerosene, it won't ignite on its own, but if it touches the sparks, the fire will flare up quickly.

For six years, there weren't any sparks of prostate cancer in you, apparently, just deep, smouldering embers biding their time, so there was nothing for the T to ignite. Once one of those embers finally sparked up, it was able to fuel itself on all the testosterone you had lying around and you had to take more drastic steps to contain it.

Analogies aren't scientific explanations, and I'm not a scientist, but does that help explain things a bit (in a simplistic way)?