Yeah, if you've paid attention in the past year, you've noticed that Morgan has not been as dangerous up top as she was earlier in her career for the USWNT. She does a lot of things well, but has been having trouble scoring. Plus, she's been injured in the NWSL.
There's also the factor that many of the really young attack players have played a lot for the USWNT since the team's disappointment in the World Cup, and they have had a lot of success.
In a World Cup year, I think she would have made the team (not certain). But the Olympic rosters are smaller than the World Cup rosters. Scoring goals was a problem for the USWNT in the last World Cup, so Hayes (the new coach of the team) has to be looking for scoring, and Morgan hasn't been that of late. The lack of position flexibility also hurts Morgan for the Olympic roster.
I'm not surprised that it was a headline (Morgan being left off the team) for many of the article about the Olympic roster being selected. She's been quite successful for the USWNT for many years, and highly marketed by the USWNT and advertisers. If you asked most American non-soccer fans to name members of the USWNT team, I suspect (can't prove it) that many of them would only be able to name Morgan from the teams of recent years.
