There are a ton of reasons to buy these items/NFTs.
Unique - Each NFT is unique, its the only one of its kind. You cannot make another NFT that is the same token number on the same smart contract. Meaning there will only ever be one of that token. This is verified by the blockchain and can be seen by anyone.
2. Copyright - Your NFT might come with copyright. If the seller chooses to do so - it means that its on the blockchain that the owner of that token would have complete commercial copyright to use that image and asset.
3. Rare - Since they are unique and cannot be copied, they are rare. Most of the time, there are very few NFTs from an artist or seller - very rarely do they have 1000s of NFTs. Therefore, you can safely assume you would be one of the few people in the world that owns an collectible item, that can be resold.
4. Collectible - These NFTs/items are collectible. You can hold onto them, and their value will only go up in price since there are little ways to dilute the collection. Buying them to resell them can earn you thousands of dollars. There are plenty of people who do it everyday and earn a living from it.
5. Downloadable - only the current owner of the NFT can download the file attached to it. Making it unlockable to the owner. If your NFT has something like, game assets, music, a PDF, or more locked inside it, you might want to buy the NFT just to download that song/PDF/etc.
6. Immutable - No one can change the metadata on the token, no one can remove your image, or the name of the token, etc. This means it will never change, it will never be removed, it cannot be taken down off the blockchain. This is what gives it so much value and collectibility
7. Forever - NFTs are forever. Because the data doesn't change, and because the blockchain is forever, you will always have that token if you buy it. You can always resell that token if you want. Its like buying a bar of gold - you own it, and you can do with it what you want.
8. Resellable - You can always resell your NFT. You SHOULD resell your NFT and trade it. You can make some serious cash trading NFTs. Some NFTs have gone for 20,000 USD + when the original buyer only bought it for a few thousand dollars. Making them over 15,000 USD in a short time in ONE trade!