I think your critique is fair (in terms of potential customer perceptions) but Delta probably decided that selling low margin group tickets was not worth the time and effort that they likely caused. The fact that you mention your price sensitivity means that (right or wrong) you are not the type of customer Delta wants to target.
The fact that they still do international - which generally has significantly higher average fares and more spare route capacity (less ability to downgauge / manage route frequency) - makes sense.