I am wondering why Planeswalker-based bonuses are primary in .

In my opinion, it's more fitting in because that a lot of the analogies that is used for the Planeswalker phenomena are . Even more interesting, or are the colors that apparently had the best chance of tracking and dealing with Planeswalkers, as Ral Zarek was able to track them in the Lightning Bug story.

On top of that, having get PW tutors over mechanically fits the colors more. is supposed to run out of options, and then lose because of it.

Blue is the color of observation and information gathering so that is why it is good at tracking planeswalkers.
White is the color of making alliances and inspiring loyalty, that is why it is good at getting planeswalkers to help.

Red might be best at igniting a spark by causing emotional trauma but that is not what most planeswalker cards represent.

I mean the emotional bond of two Planeswalkers becoming allies can also be R. R is all emotions not just negative ones.

Honestly, I would have loved to see the old tutor cycle (Enlightened/Mystical/Vampiric/Worldly) completed by a Planeswalker tutor, considering the emotional aspect Curious mentioned ("Loyal tutor"? "Devoted Tutor"?)

Red is the color of fire and smashing. It doesn't get much else.

Cato, you know I respect you, but this is a deeply uninformed stance.

...it also gets punching.

Punching is just a more specific form of smashing. Similarly, lightning is just a more specific form of fire.

Hey, in Kamigawa red got ice!

...aka anti-fire.

Ice is just fire with the hot taken out.

Punching is green, sorry.

According to my deep statistical analysis, punching is primary in green and secondary in red.

It's not so much that Planeswalker-matters cards are centered in white; it's that a lot of them have been designed in relation to the Gatewatch. Ajani's major role in the Gatewatch (as seen on multiple cards relating to him) is in gathering more of them together in preparation of the fights to come. Ajani encouraged the Gatewatch to wait for backup before heading to Amonkhet (they didn't listen), designated their meeting point on Dominaria, and took Jace away to recruit more potential members. A lot of cards were designed to show that, specifically in white because of the color's community focus.

Let's see what Planeswalker benefit cards exist (I'm disregarding cards like Ajani's Comrade that are tied to a specific 'walker, cards like Archangel of Tithes which use Planeswalker as an extension of players or card types, and the Oath cycle):

*Ajani Steadfast
*Ajani Unyielding
*Ajani, Mentor of Heroes
*Ajani's Last Stand
Arena Rector
*Call the Gatewatch
*Deploy the Gatewatch
Djeru, With Eyes Open
Forge of Heroes
Heart of Kiran
Samut, the Tested
Settle the Score
Teferi, Temporal Archmage
The Chain Veil
Will Kenrith

All of the *cards are directly tied to the Gatewatch and/or Ajani's role in it. The rest have a greater divide in color. Most are from specialty products. But if you look at it like this, white far from dominates the planeswalker-benefit part of design.

Guess it's up to me.

Friendly Tutor
Instant
Search your library for a planeswalker card and reveal that card. Shuffle your library, then put the card on top of it.

What on earth were they thinking when they printed that cycle? I mean, I know it was a rough time for MTG design, but a 4 card cycle? Sheesh.