As the saying goes, extreme claims require extreme evidence. Your statements are not extreme but they are close.
At one point WotC stated that roughly half of all campaigns were homebrew. They must think it's a pretty high percentage considering how many pages are dedicated to it in the new DMG. Even with published mods, in many cases what I've seen is the DM just mines them for ideas and scenarios but doesn't stick close to the default path. Others are designed to be played as sandboxes.
I think there's plenty of evidence for more open gameplay. You aren't just stating an opinion. This all started with you stating as a fact that open campaigns are "fringe". Now, some campaigns are going to be more true sandboxes than others but over decades of play DMs running prepared modules account for less than half the games I've played.