Spotify buys intellectual property (a podcast) and proceeds to sell access to that for a profit.
Apple invents intellectual property (the iOS ecosystem, App Store) and proceeds to sell access to that for a profit.
I love you Spotify but I don't want your ads, I don't want ads on my phone period.
I'm currently using Android, and it's just ridiculous how much my phone is demanding my attention with notifications of "Rate us!" or "Look at this emergency news! Joke, it was just an ad". They even have "let me upload all of your contacts or I wont start"-apps. Android really lets the users decide, and the app-companies sure tries every foul play they can get away with, and to be frank, giving those app-companies a smack on the back of their head from time to time as Apple is doing can be a good thing.
That said, 30% is... hefty especially when some companies don't have too.
"Does Uber pay it? No. Deliveroo? No." [1].
Even worse, Apple has taken successful apps from their Store and offer their own one. Same as Amazon but for apps.
You could argue mega corporations doing it is worse than small companies because they have way more resources to outbid competitors.