Why do we store a pair of bar magnets with opposite poles facing each other? Almost all sources I referred so far state that the proper method to store a pair of bar magnets is to keep the opposite poles close to each other, separated by a piece of wood, and joined by keepers as given in the following images:


Image source: UNPh29.1, FLINN Scientific
It is explained that, if magnets are stored in the above configuration, they retain their magnetic properties for a long period of time. The soft iron keepers help to complete the magnetic circuit.
However, I don't understand why we must store them in a manner opposite poles are close to each other. This is because, when we consider a single bar magnet and consider a plane dividing them along the magnetic axis, we get two bar magnets whose poles face each other (somewhat similar to this image). Then does it mean (due to this particular reason) that a single bar magnet by itself looses its magnetic properties with time without any other interaction with its environment? Further, what is the role of wooden piece in between the two bar magnets and why do we need to complete the magnetic circuit? 

Note: A similar question has been asked before. The post How to store magnets? discusses about the proper methods to store magnets other than bar magnets. 
 A: It's because the energy needed to make the magnet's field is produced by spinning electrons inside the metals. If the spinning electrons spin the same way they make a magnetic field, the magnetic fields from trillions of electrons of the atoms in the magnets line up and add up and then you have a force. Now the force is an entropy way of storing energy. If the energy is going to disperse even better then it has in millions of spinning elctrons, then it will try to do this.
If there is a better way for the energy to be stored, it wil automatically happen. Better way means with more quality of the energy, probably meaning it takes more space so it doesn't have to jostle as much.
So if you get the bar magnets and store them in ways that don't distort the magnetic fields at all, then the energy of the magnets doesn't need to jostle as much and will stay in its original form, and wont get disturbed.
But if you store the magents so that their fields are disturbed, and that there is force and energy required to hold them there, then bad news, there is jostling and the energy needs to store better. How will it get stored? Maybe it will cancel out the magnetic fields that caused it to force in the first place...
Just a guess...
Reference: Atkins and Paule Dekanis "Physical Chemistry 13th edition" page 769
A: Why this type of storage of joint pairs of magnets in antiparallel polarity configuration is advised is because:

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*This type of N-S-N-S magnetic flux closed circuit (i.e. using the iron keepers, material must be magnetic) reinforces their natural flow of energy thus the one magnet amplifies the field of the other refreshing their magnetization so that both magnets will last longer (magnets when properly handled can keep their magnetization for centuries). Please further read here about the magnetic hysteresis characteristic (i.e. magnetization memory) of magnets.


*As many physical systems, magnets prefer to stay at their lowest energy state (don't like to spend their stored magnetic potential energy - magnetization) therefore they don't like repulsion from an external  magnetic field that could scramble up their tiny magnetic domains alignment inside their material and thus reduce their magnetization.
It is true, magnets don't like repulsion they prefer attraction that reinforces their natural flow of energy.
Two repulsing strong magnets approached with their like poles (e.g. N to N or S to S) and left on a table free, (no hands used) will automatically reorient themselves and flip to their attracting poles and join! You can do this experiment for yourself to observe this amazing behavior as long the magnets are strong and not very heavy, preferable on a flat smooth surface.
See below video demonstration.

(magnets are wrapped in paper to protect from physical damage due clashing)
https://tinyurl.com/3n4xv83y  (video link)
Therefore, this particular N-S-N-S antiparallel pair configuration shown in the provided inside the question description photo above, isolates their paired magnetic field from external interaction  since their combined magnetic flux remains inside their magnetic flux circuit formed by the pair and does not expand out in space. Actually, the net magnetic moment of such pair is zero and they are isolated and don't interact with external magnets (as long they are not brought too close to other magnets). See illustration of the confined magnetic flux in an antiparallel magnet pair.

image source link credits: https://homofaciens.de/technics-electrical-engineering-magnets_en.htm
The two magnetic shunts or else called keepers, will further spatially confine the field on the poles since the magnetic flux is forced to flow only inside the keepers in a closed circuit and not expand to the outside.


*The wooden or plastic spacers are not necessary for pairing the two magnets but nevertheless, decreases the mechanical stress due the strong magnetic attraction between the two magnets in the pair, that could further cause misalignment of their tiny magnetic domains and decrease their magnetization. Also the spacers, prevent damage from physical contact that could damage the surface of the magnets and protect against accidental clashing.

