Images are great1, and for a certain subset of people2, they are a good way to convey information that would be difficult to do in plain text. The old phrase that 'a picture is worth a thousand words' is appropriate. I can describe how I was (let's say) standing in a park, looking at a squirrel. There are lots of details that I left out, details like: what shirt I was wearing, whether it was day or night, what the weather was like, what kind of squirrel it was, and on and on. I have to pick out the bits of information that I think are important enough to tell you about, and I'll probably miss some or I'll get some of the details wrong.
If I show you a picture, though, then all of that becomes moot. In a picture, you can see all of those details, and also every other detail that the camera picked up. Details that I didn't notice or didn't think were relevant. It's generally much more efficient to show you a picture of a thing than to describe the thing using just words.
There are also some images that aren't photographs3, but the concept is still the same. For certain kinds of information, a good, appropriate picture can take the place of many dozens of pages of text.
So, why are there no images on this site? One reason is for accessibility. If your vision is such that you can't view images, then me putting in an image might be wasting your time and bandwidth. I'll admit that I don't have much experience with browsers for visually impaired users, and, yes, I do know that if you take the time to make your site accessible that a lot of the problems can be mitigated4. Dealing with ALT tags and other accessible things can be a pain (a necessary pain, yes, but a pain nonetheless), and it's a pain that I just don't want to bother with.
Another reason why this site doesn't have images is that the kind of content that I'm putting up here doesn't need images. I know that sounds reductive, but it's true. When I work on this site, the things that I want to do don't involve me putting images up. I didn't rule them out completely, but I did find, as I went along, that that I didn't really need to put them everywhere to make the page look nice.
Those aren't the real reasons, though. They're happy accidents, and a result of the real reason why I don't put images on this site.
I originally built this site so that I could keep track of my video game collection5 when I was out in the field so that I could have an easy reference to look at on my cell phone's browswer. Sometimes cellular (or even WiFi) reception is spotty. But plain text (well, HTML and XML marked-up text) is still ridiculously fast, even on the slowest connections. I could browse this site from the equivalent of a 56K modem and still be able to check my game collection in a matter of a few seconds.
It's an art that has been all but lost, it seems. And, I know I sound like an old programmer ranting about how the young whippersnappers don't program as well as they can, and how they waste so much processing time and RAM just to do a simple thing in whatever program they're writing. But I can't help it. My formative-computing years were spent with devices that were insanely limited by today's standards, and that kind of experience ossified in my brain. This isn't to say that I don't like fancy-pants new stuff (I think some of the stuff in HTML5 is compelling), but I do prefer to make things as simple as possible to do the thing that I want to do6.
And, as it happens, this site is one of the areas where I can do exactly the kinds of things that I want to do. Where I can add only the things I want, and not add the things that I don't want. And, so far, adding images hasn't been a thing that I've needed to do to do the things I want here.