I'm pretty sure that 99% of apps on the store make so little revenue that it's not worth it to pay someone competent to review them, especially with all the ad supported free apps. So a very low percentage of apps pay for the cost of running the app store.
And after paying those $25 they are free to spam the review team with hundreds of submissions? Doesn't sound sustainable to me.
If App Stores charged a fee per submission, that would drastically cut down on spam submissions, and free up resources for those of us who actually put a lot of effort into our apps.
Once you set a fee I know apps will be updated less often, it'd be sad for open-source apps - which I'd say are the most useful of all apps on Google Play.
A fixed filing fee would level that imbalance.