IC on Digikey is 5x more expensive than board containing same IC on Alibaba: How?
Digikey sources their parts from the manufacturers and adds a retail mark up.

The alibaba seller takes remnants from someone's production run (or possibly salvaged parts, or if you're unlucky counterfeit or reject parts) they don't pay full price.

Usually it's remnants, someone makes 10000 products and has 500 parts on the last 3500 part roll left over and sells that cheap, the module manufacturer gets these cheap, makes a bunch of modules and sells them.