Package MathWorld

Yes, unfortunately, it has proved not feasible to keep the 5000+ MathWorld notebooks as well as the packages you refer to up-to-date with the latest Mathematica functionality. As a result, I wouldn't recommend trying to use archived copies of the out-of-date packages, but if there is some particular piece of functionality you are interested in, feel free to let me know privately and I can see what I can do.

I just went searching for the MathWorld packages as well and found the post you refer to in your question (Where to download the MathWorld package?). The answer there had a link that did not go to the right place, but you can still find the packages via the Wayback Machine (and actually the answer of the aforementioned post was just updated to fix its link).

In short, you should be able to download the packages from here

However, it appears that they are not compatible with recent versions of Mathematica.