I'm surprised at the number of replies on this thread lacking empathy.
Sure, DM's failed transfer is being used by the media to highlight a harsh reality which can affect footballers in transfer windows many of whom are not in the Premier League on seven figure salaries. DM is not an 18 year old academy graduate who doesn't know how football is and yes he is incredibly well remunerated in his current role. Standard media fare ("build them up to knock them down") seems to be leading to lots of negative Palace coverage right now. Perhaps this is another price of success less obvious than having your players cherry picked.
Even so I, for one, would be seriously effed off if what happened to DM happened to me. Put yourself in his position: a lack of playing time at Everton and likely what he sees as a chance to reignite his career after a career affecting injury went up in smoke with no explanation and no dialogue. He is reported to have come to London for talks and medicals, but then to have been ignored by the club with Everton telling him it was a done deal (debatable I know). This makes it seem even worse and does cannot reflect well on Palace. A theme of clerical incompetence in various forms - and which you just do not seem to hear about at other clubs - is now quite perceptible over the last 12 months.
Football is not like most walks of life and DM is hardly the first player to feel stitched up or let down. Not knowing why, and the "radio silence" from Palace, is behind his and his partner's frustrations coming out. I would imagine any contact from Palace to sympathize or apologize might be litigious in today's world, which is a pity for many reasons and does not help even if it is the right thing to do.
I think there is a lesson here clubs including Palace can learn around ways they can treat prospective employees better. Who knows when negative PR from events like this can come back to haunt us when we need players like DM more desperately than we did this window? Anyone remember the Ross McCormack thread?