On my perspective, I don't really know what is the main reason why people are spending millions of dollars for just a single art.
On the collector's perspective, maybe there is a reason for them why they are spending that much just for a single art. They want to collect it for some reasons. Reasons that I don't know either.
One thing more is that NFT's aren't just the arts, drawings, paintings that are just digitized. In-game items that can be sold too are considered an NFT. Blockchain items that can be get in the game and can be sold are considered NFT too.
It seems to me that the NFT hype will last for long. Someone sold a digital NFT house for $500,000. More information about the subject can be found here:
https://us.cnn.com/style/article/digital-nft-mars-house-scli-intl/index.html. People are making millions by selling both tangible and intangible items via NFTs. Things are going way out of proportions. I'm guessing that governments will try to regulate the space as they did with the ICO craze back in 2017. It shouldn't be long enough before everything goes down the drain.
While "immortalizing" an object through the Blockchain is a good idea, not everything is meant to be an NFT. The same applies to Blockchain technology by itself. What's happening now is an indication that the crypto/Blockchain space is still immature for the mainstream world. We're going to have to wait until governments regulate the whole space, for legitimate projects to blossom like never before. The NFT hype could become "another nail in the coffin" as people look for the next big thing in crypto. Only time will tell us whenever the idea of an NFT will become a success or a failure in the long run. My guess is that NFTs will be solely used for in-game items in the future. It makes no sense to make a digital art or a painting as an NFT as it can be easily extracted from the web at no cost. People will eventually understand this, as they put their money into what matters most.
Nonetheless, crypto behaves in many strange and bizarre ways. No one knows what will happen in the future with the crypto/Blockchain industry. Since everything involves risk, we should proceed with caution before putting our money into something as new and unpredictable as crypto. NFTs are extremely risky, the same way "De-Fi" is, and other crypto/Blockchain ventures. As long as you do your own research instead of making a decision based on someone else's opinion, there should be nothing to worry about. Just my thoughts