That shit costs money, whether it costs 30% I don't know, but given that seems to be in the order of the charges of every other store (what % of sale price do companies get on retail sales?).
The problem here is a bunch of companies have decided that they want special rules for themselves that don't include paying for services that they benefit from.
Any iOS device apple sells has 5 years of ongoing costs - software support, service upkeep, etc.
Google's store doesn't have the update and software maintenance costs, and the actual hardware sellers have demonstrate no interest in taking them on, so it's clearly not free. In fact google charges 30% on everything as well, but also makes money from all of the surveillance they have on the platform (after all, spying is how google makes its money).
Put very simply. Apple makes a profit from a sale of hardware when the user buys a new device. That's it. They continue to support that hardware for 5 years.
Google makes profit from every android device as long as that device is being used. If you buy a second hand android device then that device continues to generate revenue for google.
Despite this google charges the same commission/rent as apple.