Can someone ELI5 why there are so many posts about utxo's?

I wonder why people are even asking about this all the time? I must have asked gpt 10 times about this, but I always forget, or don't get it. I don't understand why people even care? What scenarios does it make sense to care about this?

You buy x-btc (say 1) on an exchange and transfer it. Or you buy y-btc (say 0.001 btc) and transfer it from the exchange to save the money for the future.

Ok, so what? Where does uxtos come into this picture?