My guess is that those web developers like it, want their visitors to have the same experience as them and/or implemented it maybe as a challenge or because the

My guess is that those web developers like it, want their visitors to have the same experience as them and/or implemented it maybe as a challenge or because they can. Edit: Some sites do it as part of the user experience, which might be useful, but most of the time it might be annoying due to bad implementations.