It's math
A distance based program only has 4 events to score from (1500, 5k, 10k, steeple)
Sprint based has 7 (100, 200, 400, 110h, 400h, 4x1, 4x4) plus the long jump and triple jump where there is a ton of overlap.
Even if you're being generous and giving the 800 to the distance programs, that's still 5 events to 9. In addition, it's easier to ride an elite speed athlete because they can do 4 or more events. A distance stud can do 2 max outdoors.
If you wanted to balance them a bit more an easy way would be to add a distance relay or 2 to the outdoor meet. I've always thought it was weird that they had a DMR indoors and nothing longer than the 4x4 outdoors.
If it were up to me I'd add the DMR, and then a partner 8x400 where you'd have 2 guys per team alternating laps. So each guy runs 4 400's, I think the tactics and the potential athletes would be fascinating. For example, could we get Oliver Hoare and Morgan McDonald matched up against Texas A&M's 800 guys (Dixon and Orange)?