Explain Labubu to me please

I just learned about Labubu today because my gf's younger sister wanted one. My father is coming back from China so I asked him to buy some.

They are like $8 or 55 RMB and I was shocked that each keychain thing was so expensive. But then the sister told me on the US it's $28 and sold out everywhere.

Why is this thing so expensive? In China there is an abundance and considerably cheaper. The expensive "rare" ones are only $10 converted.

Why is this thing so popular?