That is absolutely not the reason.
We have almost 10 million NFTs on Cardano, all of them run on IPFS. None on Iagon (except for a few tests that I did).
This could change in the future but as it stands right now, Iagon is not relevant for Cardano NFTs. That's why it's a very good step to partner with a different chain to create more resilience for the existing NFTs.
This in no way hinders a future integration of Iagon...