Since the Delta/LATAM partnership makes MIA much more strategically important in the DL network, I wouldn't be surprised if they resume LAX/SLC-MIA and start SEA-MIA, all once daily to facilitate SA connections.
Facilitating LATAM connections at MIA has a few BIG problems. (Relying on a Wikipedia MIA LATAM destination list and ITA Matrix schedules for the week of 1/5/2020.)
1. There isn't a single daily LATAM destination from MIA that isn't already served by DL from ATL - not one.
2. LATAM has quite the range of departure times from MIA. (Maybe they could consolidate them but they haven't, suggesting aircraft utilization, slots availability, gate availability, or local market time-preference issues.)
destination, MIA departure time, frequency
REC 1730 Th, Sa
FOR 1630 xTh Sa
GRU 0805 daily, 1710 daily
LIM 0100 daily, 1640 daily
EZE 2015 daily
Belem 0205 Su Tu
PUJ 0825 Su 0845 Sa
So, how do you want to schedule DL's new incoming flights to connect to these, over that 17-hr departure window? From what U.S. non-hub cities can you rationalize new DL flights to connect to a few non-daily flights REC/FOR/BEL?