Perhaps the proprieter - who is doing all the work themself, for free, giving it all away - is trying to cover expenses?

All books on this site are free.

... a one-woman operation that has been running for over eight years. I format every single ebook myself, as well as maintaining the website. This is a passion project that was born from a love for reading and a commitment to make free ebooks that look good and feel enjoyable to read.

I literally just spent $25 on a bunch of bandcamp albums that are "pay what you want" (I could have put $0) just to support the artist. Sometimes supporting people is just a cool/good thing to do.

Your argument in a nutshell: "But I can steal it easily, why do I pay?"

I think that's one of the reasons I won't be writing a technical book.

I think all books should be free for everyone. You'd get less moron and criminals that way.

There are fewer morons and criminals on the free internet? Hmmm ...

This argument could be applied to the majority of media platforms and plenty of people pay a lot more than £40 once off for those.