I don't see how respecting one's rights (in this case one's copyright over his own works) leads to having revoked the right to buy books.

I agree that it is sad to see many online book stores moving from "selling" to "renting". But that is a completely different problem.

As a personal note, I know the pain of not being able to access scientific papers because they were behind paywalls, and I had to search for drafts to be able to read them. But that model was well in place circa 2010, thus it's and old tactic applied to a new field: books (and others).

Software performance, which translates into CPU/memory/disk resources, are only one aspect of the costs incurred by crawling bots, and fall under the unmetered / virtually infinite category. However, there are also the metered resources, that do translate (after a certain threshold) into monetary costs: network bandwidth.

Thus, regardless how well one optimizes his site delivery (static site, minimizing, CDN, caching, etc.) a stampede of bot crawling does in the end become a DDoS, which if it doesn't take down the infrastructure, it might leave a deep hole in one's budget.

For example, for one of the sites I manage, I get daily peaks of ~300 requests per second measured at the backend, for a site that already employs heavy caching (both client-side, CDN, and even server-side). This wasn't so a few months back, and the site didn't just jump in popularity.