IPFS only enables decentralization, it doesn't guarantee it. I'd be willing to bet most NFT content is only pinned by the exchange.
Many NFTs that reference an IPFS url point to a specific IPFS gateway run by the creator as opposed to a “standard” IPFS url with ipfs://
I know this because I have a product that indexes various blockchains and the referenced content.
Would you be willing to share some numbers on what you're seeing? This is valuable information.
OpenSea engineers should be shamed for their use of HTTPS URLs in contracts, but it is not the norm outside of their minting platform.
In any case across the 70 million or so NFTs I have indexed HTTP is definitely the majority.
it would be worth taking a sample of higher value tokens that are not minted by OpenSea. probably the vast majority of those tokens are spam or bots trying to capitalize on existing web content like DeviantArt database.
better platforms like Manifold, Foundation and Zora are already using IPFS or Arweave
if effective storage proofs ever become a thing, then the later half (decentralized storage) will be standard