It's essentially random, so having 100 flights increases the chances of you having at least one SSSS overall, but for any particular flight it's the same chance, so some people may only ever take 1 flight and get SSSS and some people can do 200 flights and never have it. It's not personal, and it's no reflection upon anything you have done or not done. I suspect some people get SSSS and not even realise it - they would just see it as a bit of extra security at the gate, less intrusive in some ways than main security.