I want to understand *exactly* what React has, that Preact doesn’t have?

Preact is 4KB gzipped, while React is 43KB. Preact is hailed as the light weight alternative; but before getting into bed with Preact; I want to understand what I would be missing exactly?

P.S.: I know about preact-compat

(Love the cute Santa on Hashnode logo! Merry Christmas, everyone! :D)