In the case of Mingle/Trello specifically these are closed source

(possibly externally-hosted) software infrastructure pieces that we, as
a Foundation, do not want to have an ongoing dependence on. During
project creation and early development, the deadline-formation and other
management tasks these afford are sometimes necessary in commercial
space but do not really exist in all-volunteer open-source efforts, so
some degree of dependence when there aren't open-source solutions
becomes a necessary evil for that time in our project development.
However, an ongoing dependence on these tools would become a wall
prohibiting certain members of our community from being able to fully
participate in, and that would be contrary to our commitment.

I agree these tools are problematic for this reason.  I understand why
some people currently choose to use them, but the Foundation should
investigate free alternatives that can meet our projects' needs.