The source code of this website is available under the MIT License. That means you have permission to modify and distribute it for both commercial and non-commercial use. The source code is currently available on GitHub.
The current theme for this website, Engimo, is also distributed under the MIT License.
The non-code content of this website, except as otherwise noted, is available under the Creative Commons Attribution-ShareAlike 4.0 International license (CC BY-SA 4.0). That means you are free to share and adapt the original content on my site, even for commercial use, as long as you give me attribution and release any derivative work under the same license.
The real question is why not? I don’t really stand to gain anything by restricting the license, and I generally believe that the Web is a better place when people are allowed to share, reuse, and remix things. I’ve been inspired by other sites that similarly offer free licenses to their content, and I want to do the same thing. If you find something on this site that’s useful to you, I don’t want to stand in the way of your making something great out of it!