Coach's decision is the simple answer. Rather easy for the girls, as there were 2 teams in Cottbus and everybody knows who won.
I think what's important is to have the financial commitment to fund 8 athletes for men and women, rather than just the top 4 from 100m nationals plus whomever else gets in the list. Let them go to Europe, race together, train together in the pre-championships relay practice. But fund 8 athletes for the whole season, not 4 or 6.
I have no doubt that if we sent the second place TEAM from Cottbus into the semis, USA would have won the gold in the womens 4X1.
Somewhat similar situation in the mens semis, where Mike Rodgers is relatively inexperienced, had problems with the pass, Shawn had to slow way down, then Doc doesn't get going soon enough (perhaps overcompensating) and Shawn touches him before the zone.
Both DQs come down to inexperienced individuals, in my opinion, and we certainly have the depth of talent to fix this.