I've added a discussion of Tidelift's share to the docs at https://tidelift.com/docs/lifting/paying TLDR our commitment is to pay out at least 50%.
What we're doing at Tidelift is an enterprise software product (analogous to something like Red Hat Enterprise Linux), but a difference is that instead of hiring a bunch of people to repackage upstream projects, we're offering upstream maintainers the _option_ to participate directly by helping us do the work - for a revenue share, rather than a flat fee.
The app store analogy isn't quite right; an app store provides a catalog and some review services, but much of their 30% rake is profit as far as I know. The Tidelift share includes funding all the non-engineering parts of an enterprise software business, including a crucial one, a sales team.
The point of this is to make the pie larger. We want to pay the maintainers (at least) 50% of a lot of money, instead of 90% of a little money.
btw there are a number of options out there to make straight donations to projects and we support those! That isn't mutually exclusive with what we're doing here and in fact many of our participating maintainers also take donations.