Clearly, if it was unlawful entirely, someone might by now have sued someone else, and there is none of the sound and fury which would normally accompany such an action. The first and most obvious reason is that cacheing is, in general, welcomed. Access is speeded up for everybody, and the general theory of a web page is that though copyright inheres, for businesses it is in the general nature of an advert. I should not complain if someone takes my advert and re-publishes it for me. There are one or two reasons why caching may not be welcomed by the web-site owner Most web sites make whatever money they do make because people visit the page.
More visitors means more money.
More caching means less visible visitors. A site owner may make a mistake on his page, or his page may be time sensitive. We, for example include some figures representing our professional fees. These change from time to time. We would not want to change our prices, only to discover that somebody comes to us on the basis of figures which are out of date.