It appears to me that Google recently change the criteria for appearing in alerts. They made it much stricter. I have alerts set for my own full name and my brand name. I used to get several alerts a month, most of which were junk. Things like '<your brand>.com on <stupid domain rating site>.com'.
I haven't had those in a while. The only thing I got this month was when I change my StackOverflow account to use my full name rather than a nickname. I got a google alert on my full name for my profile page. I didn't get alerts on the other stack exchange sites where I also changed my name, nor for any of the questions and answers on any of the sites where my full name now appears.