Well the difference is that most fans don’t mind paying the money to get those items, they don’t typically just hand him money for nothing just because they like him. Twitch subscription is like a concert: you get something in return, but donating large amounts for nothing to already successful streamers is a bit odd.

But not that odd: I’ve backed people on patreon because I liked what they do and wanted to reward them - even though they were already making good money on it - and then never actually accessed the rewards. So I do get it.

Presumably those fans are buying those things at least in part because they want to have the album, concert experience, or merch. With twitch donations/tips you get comparatively very little in return - your username might pop up in a video overlay for a few seconds, and the streamer might be like "hey thanks, [username]!". Those 3-4 seconds are typically the entirety of your several-hundered-dollar experience.