Why can’t you make the website offline

Perhaps you are looking to read specific webpages while you are “offline” without access to a network connection? If this is your intention, you’ll need to add the webpage(s) to your Safari Reading List.

Save webpages to read later in Safari on iPad - Apple Support

What website are you referring to? Besides, you do know the idea of website. The keyword here is web. If you are referring to something else, please explain.