How YouTube channels make money
Ads pay after the channel qualifies
Until the channel meets YouTube partner rules, ad money is not available. The early videos are there to find a subject people finish watching.
Memberships and fan payments need a reason
Viewers pay when the channel offers something they cannot get from the free video. A join button with nothing behind it does not create income.
The description is a storefront
A video can point to a product, a service, or a later affiliate offer. The video still has to be worth watching if the link were removed.