Says SI.com:

Philly needs as much shooting as it can get, and Johnson fits them to a T as an experienced college player who could comfortably plug in on the wing sooner than later.

He’s 23 and comes with an injury history, but the age factor might be appealing for the Sixers, who have to explore low-cost pathways to improve their star-heavy roster, with the hope being to retain Jimmy Butler and Tobias Harris.

Johnson is an outstanding catch-and-shoot player with little to prove in that regard, and seems like a natural fit at this pick.

https://www.si.com/nba/2019/06/11/nba-mock-draft-zion-williamson-ja-morant-rj-barrett-pelicans-grizzlies-knicks-anthony-davis-trade-rumors