Surely you are not serious?
Why do the world's best pro teams invest markedly and increasingly in highly specialised 'mental skills' and 'sports psych' coaches?
Of the 20 or so reasons, one is certainly to deal with the dimensions of human athletic skill in team sports of exactly the type and kind to which you refer.
'Mental aptitude and concentration' (your words) in demanding elite team sports can be affected by a huge range of alterable human psychology, S&C and team culture variables: fatigue, low inner psych confidence team-wise or individually, unclarity in preparedness and tactical agreement within a team as to how respond and play, poor team morale, an excessively individualistic micro-culture within the team that mitigates against close-in player-to-player trust, poor preparedness to handle pressure contexts, etc, etc. These and other related variables can all be managed and potentially improved by the right type of insight and specialist coaching support.
To say these parameters 'have nothing to do with coaching' (you are of course I assume an expert in such matters in speaking so boldly as you do) is, bluntly, a 1980s definition of team management thinking to put it most politely.
If you fail to grasp my points, please carefully study the NZ rugby career of one Glibert Enoka, the Mental Skills Coach of the ABs (and now taking on a far bigger role across all of NZ rugby) in just this area of expertise. To get started re Enoka and what he thinks and brings have a look at:
https://www.gameplan-a.com/2017/03/make-mental-strength-your-strongest-skill/
There's much more available re his seminal work in this area re the ABs. Why do we think they are so sustainedly successful? One reason: in their coaching capabilities they map every critical performance and skills parameter and detail, not just some.
I have been saying for years here and otherwise that Australian elite rugby - and especially the Wallabies - need our own version of Gilbert Enoka.
Mental skills, team culture (in the deep not superficial meaning of that term) and individual player psych development are simply a huge part of building successful teams and more particularly sustainable and repetitive success vs 'every 20 year one-off outliers'.
And moreover the inferred notion that somehow the 'players should take responsibility and just sharpen up and fix these issues themselves' is a combination of (a) the utterly naive (humans in teams rarely fix their own mentally- or team culture-based based frailties, they almost always need assistance of one type or another particularly in even becoming aware of what is happening to, or inside, them) and (b) passively abrogating the clear responsibilities of modern elite HCs to diagnose attitudinal, emotional, cultural, confidence, concentration etc etc issues within their teams and subsequently engage the right specialist resources to fix them.
Waiting and hoping that such problems and deficiencies will just auto-magically fix themselves with a win here and there is a reckless, high-risk HC strategy. Assuming you want your RU to avoid bankruptcy, that is.
That's all well and good, but how did teams of the past cope without mental skills coaches? How did the Wallabies concede only 1 try in RWC 1999? How did they close out games against the ABs with regularity between 1998-2002? I appreciate that things change as sport evolves, but you can't move too far the other way and put aside the responsibility of players for their own application, attitude and aptitude. Some of the deficiencies we are seeing repeatedly in the Waratahs, and to a degree in the Wallabies are in very basic functions that any player at this level should be able to execute without needing someone to focus their rugby-intelligence upon it. I agree, a long term pattern of success is more likely with all aspects being attended to, but players clearly can, and should, be able to motivate themselves and focus themselves upon the skills for which they are highly paid.
A coaching issue? Of course.
A player issue? Equally, of course, in my mind.