I think a lot is determined by cost as well. If decentralized ends up providing the same product or service (more or less) but at a cheaper cost, that will be a main driving force for people to go decentralized. After all, it was one of the selling points of Bitcoins -> no middleman to take a cut in terms of transaction fees, so it was cheaper than traditional methods of sending.
That went out of the window ofcourse when the fees got high, but still it's important: the blockchain variant needs to be better in some way, and cheaper is one of the more obvious forms of better. If it ends up being only slightly cheaper, then consumers may end up using centralized platforms after all... there are some benefits to that too in terms of provided service and warranty etc.
But yes, this uncertainty is why I stay away from 'decentralized ebay' projects and such. No guarantees they're actually going to conquer the userbase.