discoverability, if a friend talks to me about a podcast I could be interested in, i'd rather just have the name of the podcast than a full URL.
Here i can just use any podcast app that integrates with Apple podcast service and type the name of the podcast i want to listen to.
Your question is the same as: "Why do you care if $YOUR_SEARCH_ENGINE (google, kaggle, duckduckgo) hosts a list of websites?"
sure, you can use google or a search engine, look in the results for the actual feeds url (vs just a website or something), and copy paste it in your podcast player.
Or you can just search from it directly in your podcast app.
not to mention that unless the podcast has an official site, a Google search for the feed will turn up 10 different mirrors of the feed, without any clarity about which one's the canonical source.
in the past i've subscribed to a dead feed this way i think because the author changed who they syndicate through. i assume Apple's directory is maintained in a way that largely avoids this (simply by it being the canonical directory).
Your question is the same as: "Why do you care if $YOUR_SEARCH_ENGINE (google, kaggle, duckduckgo) hosts a list of websites?"