Games could still do this (via a single one-time "microtransaction"), and some do this. But standard microtransactions are stupidly profitable, enough to tempt most devs.

And, frankly, the gaming industry at large has proven that paying up front does not prevent microtransactions. Even in mobile games.

I always wondered why Apple can't implement something similar to Steam refunds.

Quote from https://store.steampowered.com/steam_refunds:

You can request a refund for nearly any purchase on Steam—for any reason. Maybe your PC doesn't meet the hardware requirements; maybe you bought a game by mistake; maybe you played the title for an hour and just didn't like it.

It doesn't matter. Valve will, upon request via help.steampowered.com, issue a refund for any reason, if the request is made within the required return period, and, in the case of games, if the title has been played for less than two hours.

They don't even need to do much, just add a category for developers who want to have a free + single-IAP-to-unlock-the-whole-thing version, and let people search that category specifically. No need for Apple to enforce time limits or anything. The trouble now isn't that demos can't exist, but that it's hard to tell which IAP-bearing apps are just full version unlocks and which are whale-chasing bullshit.

For that matter, just segregating games with any "consumable" IAP from those without would probably help a lot.

Mismanagement? Do you realize some people spend tens of thousands of dollars a month on in-game micro transactions? Yes I do mean individual people. These people are basically the entire revenue stream for the Play Store. Of course they're not going to discourage that business model.

On a less discouraging note, there is a "try now" button in the Play store that games can implement. You can upload a lightweight version of the game for people to play without installing / paying for the game.

It's not a well-supported/advertised path, but you can always download a pay-for game for an hour and then get a refund if you don't like it.

Google at least used to do automatic refunds if you uninstalled a pay-for app very quickly - I once had that happen with a utility app that I used to convert some stuff - since it worked exactly like I wanted, I re-purchased and left it installed for a few days.

It still wouldn’t help. There is nothing stopping a developer from releasing a free game with a single in app purchase that unlocks everything.