I agree. From a beginners perspective it assumes prior knowledge of why this is done.
Tonicising" each diatonic chord with its own II V turns it into a temporary key.
Using just triads this was the first chromatic harmony going back to Bach's system.
Why? It facilitates movement to remote keys giving a sense of variety and movement away from and back to the main key. Using the first inversion of the dominant triad of each scale harmony gives chromatically voice led sequences; moving through the key using all 12 degrees.
I.e. Cmaj/AMaj/C#/Dmaj ..etc
So that gives you license to break away from a possibly uninteresting strictly diatonic progression.

Jazz standards add extensions to the II Vs influenced by the Romantic era but its the same system. The difference is that by the late 19th century the major and minor keys on the same tonic were used interchangeably to further increase chord possibilities and ease of modulation.


It also allows for the use of all 12 notes melodically in any key so that non-chord and non-scale tones can be used as tensions that resolve by half step to a diatonic tone.

This kind of quickly resolving tension is characteristic of jazz standards.
Post 1960 originals by jazz composers is mostly a different ball game altogether.

Yet search for Ralph Towner's lovely composition ' Hand in Hand' to see how very overt use of the Bach system can still be used to telling effect today given a few modifications in harmonic colour.