Considering the author of this font pretty much made it for their own use, the answer to your question becomes: because that's their personal preference. No one needs to justify what font they prefer.

Then they decided to be nice and share it with the world for free.

Thank goodness the idea that something is free must automatically shut down any criticism hasn't taken over. We wouldn't have anything good.

Not sure how you drew that conclusion. But asking "why <subjective aesthetic preference>?" is not going to get you anywhere. Someone made a font for their own use because they personally enjoy. They then shared it for free with anyone else who might also enjoy it. There are certain color combinations I prefer for text and background that other people probably hate. I couldn't tell you why I like them, though.

Readability can be generalized (tiny text is almost universally difficult to read) but it's also very much a personal thing in other ways. You can criticize one's preference all you want but it hardly seems productive. I get a lot of flak for preferring green apples to red apples, but no amount of convincing will change my mind.

>Which only moves the question back a step. Why, exactly, make reserved words, comments, tag attributes, etc., explicitly less readable than the rest of the painfully wispy text?

I have no insight into the author's mind, but I can only assume the answer is, "because they prefer it that way." Why else would they have taken the time to do so if it's for personal use?