The concerns for them were safety. They were walking downtown one night when one of the shootings occurred nearby which shook them up. They also feel like the problems with homeless or mentally ill people accosting people aggressively is beyond what they're willing to tolerate.
Full disclosure: this couple grew up in white, affluent suburbs. They thought it would be cool to live around downtown and have now soured on it...
I agree with previous commenters that this is just one anecdote, but it does beg the question of the prevailing narrative and if young couples like this who come from the burbs don't stay, while offices shift more towards suburbs, the progress made can erode very quickly.