I used to get that question all the time! I don't get it so much anymore, now that I've been married for nearly 11 years & over 30. Unfortunately, I think the reason that people have quit asking is because at this point, they probably assume that I can't have kids since I've been married for so long & have remained childless. I LOVE babies, but I don't want children. Partly because I don't want to raise children in these trying times, partly because the fact is, I like babies & small children. Once they get about school aged, they aren't as appealing to me. I like when they are small & you can hold them & they will just cuddle up in your lap. I have a 2-year old nephew & we have fun with him; buying him toys, clothes, etc, but we don't have the day-to-day stress & worry that comes with actually raising a child. Some people may say that's selfish, but I disagree. It's just being honest. And, IF it is selfish, well then all the more reason that I shouldn't have kids!
Little side note: when I was about 24, & getting the "when are you having kids" question on a regular basis, I got really pissed one day & told someone that I couldn't have children. She was all like "oh, I am SO sorry!" & then I felt like a turd for lying like that. I never did that again.