Is that not just youtube "memberships" though? The creator can choose the cost and have multiple "tiers" - I don't think there's anything stopping them having a $1 "tip jar" tier.

Sure, it's not quite the same, but at some point of similar-enough the number of people who actually use each feature becomes vanishingly small and/or the cost of managing the extra option outpaces the income, and it's just not worth it.