Why doesn't this happen to me, and indeed the rest of my crew?
I don't know, but the science says that you are an exception.
The Chartered Institute of Environmental Health released a study in 2004 titled "Common cold transmission in commercial aircraft: Industry and passenger implications"
The Chartered Institute of Environmental Health - JEHR - Common cold transmission in commercial aircraft: Industry and passenger implications
Reading the study I am wondering if stress and fatigue are greater contributors than we realize. If you have been doing this for 35 years you obviously enjoy it and will find it less stressful - god forbid even enjoyable - than even the most frequent pax (like me sadly). That would explain the fact that as a cohort cc have anecdotally fewer colds than pax.