Because Uniteds site is easy enough for a 3 year old to use.
Try some of these options, searching segment by segment. (The LAN stuff on ba.com)
1. LAN -- MIA-GYE/UIO
2. AA -- same
3. AA/LA MIA-BOG/CLO/MDE-GYE/UIO
AA.com should help with the domestic stuff. Sometimes there are DFW flights too.
LAN availability isn't great and doesn't seem to be updated frequently.