Library Fraud?

In a recent post, several people pointed out that a library worker questioning the name on a trans person's card is likely not transphobia, but related to "fraud".

What kind of fraud could someone commit by taking out a library card in a name that isn't their legal name? Is this really something that happens? I'm truly curious.

The only thing I can come up with is the desire to have multiple cards so as to avoid paying old library fines. But a lot of systems have moved away from fines, or from using them in a punitive way. And surely fine-avoidance is a less likely occurrence than having a patron who is transgender, or any potential issue with whether a worker, personally, feels like the name on the card doesn't match the person checking out a book.

While, as an avid reader and an absent-minded person, myself, I get the temptation to take out a new card to avoid old fines, this surely isn't a major source of concern for libraries. It's not like people are using this to rack up thousands in fines. The largest library fine I've ever had to pay was like $60. I've also dealt in secondhand books in my spare time, so I can tell you for 100% sure that no book in circulation at a public library is valuable enough to commit fraud in order to check out and resell. Panhandling would probably be more lucrative. Hell, going over to the research library and pocketing rare books till they figure it out and ban you would make more sense.

Besides, why would someone go to the trouble of getting a second or third library card in a different name, for crime, but blatantly choose a name that doesn't correspond to their gender? Wouldn't that increase the likelihood that their fraud would be discovered?