[1] https://www.claymath.org/millennium-problems/yang%E2%80%93mi...
The mediator of the strong force, the gluon, is a different beast compared to photons. It can directly interact with itself and create more of it. Add in the math that describe it and you get an emerging behavior vastly different from the one you get for photons.
The article also mentions mass-growing at a distance, I wonder if - they really mean "with displacement, mediated by speed" - there's some interaction under which two gluons can enter a binary, uniform rotation about one-another
The introduction to the full text identifies a subset of the theories under comparison, and hints at the techniques the theories deployed to arrive at their predictions, for example by "light-front quantized QCD" [1]
This running of the coupling constant would in principle allow unification with the electroweak force in most theories e.g. supersymmetry - we just have not worked out the exact framework.
The fact that the force between hadrons does not decrease with distance like the electromagnetic or gravitational forces explains why it is impossible to obtain free quarks.
When you have a system of particles which is bound by electromagnetic forces, e.g. the electrons bound to a nucleus, and you come with an external force and you pull the electron away from the opposite charge, the force retaining the electron becomes weaker and weaker while the distance increases, until the electron becomes free when the work of the pulling force exceeds the binding energy.
On the other hand, when you have a system of bound quarks, e.g. 3 quarks that compose a proton, and you come with an external force and you pull away one quark, the force remains constant while the distance increases, keeping the quark bound, until the work of the pulling force exceeds the energy of generation of a quark-antiquark pair.
At that threshold, a quark-antiquark pair is generated and the antiquark sticks to the quark that is pulled away, while the quark sticks to the other 2 remaining quarks.
Thus the effect of pulling one quark away is not the appearance of a free quark, but the appearance of a free quark-antiquark pair, which is named pion, a.k.a. pi meson, while the original proton may either transform into a neutron or remain a proton, depending on what kind of quark-antiquark pair happened to be generated.
To prevent the existence of free quarks, it would be enough for the force to decrease very slowly with the distance, but a model where the force is actually constant is the simplest and the most elegant, so it is good that the experimental data match this.
The reason why the interaction through electromagnetic or gravitational forces has a force decreasing with distance is that the force is the same in all directions and it is constant per solid angle, so the ratio of force per area decreases proportional to the area of the sphere centered on the source of the field.
This can be visualized with the Faraday's lines of force as equidistant radii going from the center of the sphere, and the density of lines of force per area decreases for greater spheres.
On the other hand the force between quarks can be visualized with the Faraday's lines of force not being towards all directions but being confined inside a tube that connects 2 quarks. When the distance between 2 quarks increases, the tube of lines of force becomes longer, but its cross-section remains constant, so the density of lines of force per area, i.e. the intensity of the force, remains constant.
When the distance increases over the threshold for generating a quark-antiquark pair, the tube of lines of force breaks into 2 tubes, with the 2 new ends of tubes being terminated on the newly generated antiquark and quark.
So visualizing a force that is constant with distance is not difficult and there are many materials that have the same behavior when they are extended over their elastic limit, i.e. their elongation increases continuously while the force is constant, until the material breaks.
There is actually a simple way to obtain a force between two objects that does not decrease with distance: simply connect them with an (idealized) string. And it is indeed not entirely inaccurate to say that the strong force produces some kind of quantum mechanical string between two quarks.
Historically the study of exactly these strings for the strong force led to the idea of string theory. Only later was it realized that it can be useful as a theory of quantum gravity as well.
Gauss's law (which is purely mathematical). Or basically, the area the force "sees" as it gets farther or closer.