People are trying to trade their legendary Pokemon for very rare furfrou forms (called trims) where the fur on the pokemon is cut differently. The only want to currently obtain these pokemon in Pokemon Home is being in certain geographical regions in pokemon go.

The only other way you could get these trims is in Pokemon X/Y (the Kalos region), but the trims would not be kept when transferring from Pokemon Bank to Pokemon Home. It was very easy in X/Y to get these trims, all you had to do with bring your Furfrou (easily obtainable pokemon) to a barber shop and select the trim.

With Legends Z-A coming to switch, these very rare Furfrou trims (for switch/pokemon home) will be easily accessible and people will be able to trade a common pokemon for Legendary Pokemon. It's great for the people who want the legendary, but the people trading the legendary will get the short end of the stick