SD is my second team and I'm devastated to see Reyes go.
From what I've read, the Padres wanted their future center fielder, more lefties in the lineup (including Josh Naylor in LF), and more OBP/speed for the top of the order.
Future lineup could look something like this:
1. Trammell CF (L), 2. Tatis Jr SS (R), 3. Machado 3B (R), 4. Hosmer 1B (L), 5. Renfroe RF (R), 6. Naylor LF (L), 7. Urias 2B (R), 8. Mejia (S), 9. Pitcher