...Both projects have their own coins: STX (Stacks) and SOV (Sovryn).
We need something without other coins. The reason? If these coins / this network don't exist anymore ... so your NFTs won't. But Bitcoin will exist ... always.
We don't need more coins in the market. There are no reasons to create more.
This is the first time hearing about those coins STX and SOV and if they will become popular then wait for thousands of other coins built just for the NFT market. Note that those coins doesn't represent independent networks having their own blockchains.
I would always recommend the actual networks and try to develop them .
AFAIK Stacks has his own blockchain that is tied somehow to the Bitcoin blockchain to secure everything. Their coins (STX) can also be mined by Bitcoin miners for extra profit if I understood correctly.
I think Sovryn has his blockchain too like Stacks but I not 100% sure. I will have to double check that..