Perhaps I'm just uninformed about the business model of trading card games like MTG, but don't they need to set these rules for game stores to incentivize players to actually buy real cards to play with? Sure, not every player participates in tournaments like these, but I imagine there is a non-negligible amount of money spent by dedicated players who want to keep up with the competition when new cards release.
Correct, they used to display regular ads on their website (but never in the actual games) for those users that did not purchase the Premium subscription. Users with the premium subscription would then see only user-created ads for user-created content.
It was honestly quite jarring and this new approach is better for developers on the platform, as they can reach way more people.
Very annoying, but there is a relatively quick workaround for those that don't know: On Chrome, Inspect the page and go to settings, then click 'Disable JavaScript'. Reload with Inspect open and you should be able to bypass most paywalls.