Their FAQ lists multiple reasons that various countries, ISPs, etc. block CatBox, and using a VPN is often mentioned as the solution. Here is an archive of their FAQ that you should be able to read from any connection:
https://web.archive.org/web/20250822215754/https://catbox.moe/faq.php
What is the value add of this product? The donors and recipients still need to set up a Monero wallet and everything to use the service. A recipient may just as well instead use any other means (social media, etc.) to announce that they are accepting Monero donations at xyz address.