Some reasons I can come up with are:
- Lack of time
- Lack of expertise
- Personal preferences

If everyone here whose question gets answered took some time to give back to the community what they received, we wouldn't have this situation cropping up. Instead people post their questions, get an answer and take a leave never to show up again unless they are confronted with yet another question.

It's also interesting to notice that the questions posted by regulars have less probability of getting by unanswered as compared to those posted by newcomers.

PS: Consider snipping your fake signature, you can add a signature to your profile which shows up with each post from the Control Panel.