Agreed, and I hope it will become more popular. But right now, since you can't browse IFPS with firefox or chrome, and manual minting is harder than clicking a button on open sea, I wager private platforms will keep their appeal.
Maybe when decentralized service will do all the decentralized hard work for you, take your metamask, upload your content on IFPS, mint it, then let you sell it, it will take on.
I think the key here is that we've already as a society given up a lot of our ownership for the sake of convenience. Most people buy their phones through a mobile carrier, locking them in through the life of their contract. I'm not totally sure about how Google accounts work, but I'd wager that getting your Google drive data back if you're banned is difficult. Kids these days are even purchasing skins for video games with the full knowledge that if they get banned, all of those skins will be gone.
A lot of what we own these days is not "owned" in the traditional sense. Opensea is no different from purchasing a video game that you could be banned from in that both purchase prices aren't ownership, but rather a price to access a product.
Actually this is quickly becoming the standard. Once you mint an NFT on opensea, you have the option to "freeze" the metadata, which transfers the image and everything else to IPFS storage.
Maybe when decentralized service will do all the decentralized hard work for you, take your metamask, upload your content on IFPS, mint it, then let you sell it, it will take on.