Why don’t hashtags work on Instagram?

some time i think why hashtag did not work in instagram just like facebook i have an e commerce store on facebook and instagram But i have got more sales result from facebook comparing to insta

Every hashtag does not work the same. Some can give you enormous reach and some could not even reach thousands.
So depending on the niche of the account, one should make hashtags set and keep trying and analyzing which hashtags work great for them.
Finally, I would say Instagram hashtags work only thing is we need to pick the most relevant ones,