Local sales taxes are sometimes earmarked for a specific purpose that improves the local community. For example recently voters in the Los Angeles county approved a sales tax increase to fund new Metro lines [0]. It seems fair that since this Metro line primarily benefits residents in this region, this additional sales tax should only be charged when one buys products in this region (primarily residents). Concentrating all the money at the federal level and then redistributing doesn't seem very fair.
[0]: https://ballotpedia.org/Los_Angeles_County,_California,_Sale...