I believe one reason they do it this way is that they want to ensure that they stay firmly in the realm of donations and might not inadvertently move to selling

I believe one reason they do it this way is that they want to ensure that they stay firmly in the realm of donations and might not inadvertently move to selling stuff (by creators starting to provide benefits to people who donate). This is a key difference from Patreon. Selling stuff comes with lots of different legal requirements, which is why e.g. Patreon will deduct VAT for European patrons. Similarly, having a (relatively low) limit on maximum donations I imagine is done to avoid running into anti-money laundering regulations (which are particularly strict in France).