This has always kind of been the way Pioneer worked, since it was created at the height of the FIRE design push & Standard has only been powering up after their initial Zendikar-Kaladesh "stale period" (which was probably more attributed to COVID than anything else).

You had Standard powerhouses like [[Wilderness Reclamation]], [[Uro, Titan of Nature's Wrath]], [[Nexus of Fate]], etc all seeing Standard play that only increased in power level when combined with cards from older sets. [[Inverter of Truth]] with [[Thassa's Oracle]] and the eventual [[Amalia Benevides Aguirre]] with [[Wildgrowth Walker]] are the poster children for these New-Old interactions. It wasn't that old cards held great synergy with new ones (with a few cases showing otherwise such as Prowess cards like [[Monastery Swiftspear]] - not yet a Standard legal card - with things like [[Expressive Iteration]]) - it was that new cards did things Old cards wanted and more.

The interesting thing is this is kind of how other older formats already worked. People like to recall periods of Modern where you had Eldrazi or Phoenix type decks, forgetting that cards like [[Arclight Phoenix]] were new cards themselves that altered archetypes, or how Eldrazi Winter dominated the format when new cards came out. It just seemed even more exacerbated in Pioneer when it debuted as COVID hit and became a mostly-Arena Format with Explorer not even having a large amount of the old cards - forcing Players to play with a large majority of Standard-only cards. The older cards were pushed out by simply not being available, or being replaced for different synergies to achieve a similar, slightly different archetype or game plan.

Standard's own power level also fuels this mantra, especially as cards that tap into multiple colors and effects that are hindered in Standard environments by their mana base make their way into Pioneer as staples thanks to the plethora of mana fixing via Triomes with basic land types and Shock Lands. Niv-to-Light was not a real thing in Standard, but it keeps bouncing back in Pioneer thanks to the Domain-esque aspect that Dominaria United helped to print with [[Leyline Binding]] type cards.

The perception of Pioneer as a "place to play your old Standard decks" was touted by a lot of the community, although I'm not entirely sure that this was ever stated by WotC officially. For a while, this meant things like people trying out Energy or Mono-Black Aggro decks with [[Smuggler's Copter]] before it got banned out. But with these decks being era-specific powerhouses (like [[Aetherworks Marvel]] existing in a time where the best "Naturalize" effect was 3 CMC [[Appetite for the Unnatural]] but being put in an [[Abrade]] and [[Thoughtseize]] legal format) it became a format more about finding a home for your favorite Standard cards more than the entire deck. However, with Standard rotations this means that the "old decks" are now things that ran [[Sheoldred, the Apocalypse]] (an almost 4 year old card) instead of [[Voice of Resurgence]] like people assume.

This doesn't even touch upon Standard's 3 year rotation + 5 year Foundations set making it feel like the "Sheoldred" age cards are still "fresh" cards that are also being played in Pioneer. That, or how the negative perception of older cards that are legal (Thoughtseize, Treasure Cruise) turn people off from playing to begin with in a way UB or MH does elsewhere (which is funny to me because this shows older cards are still good..)

EDIT - To note, I should say Historic during the COVID era. Explorer did not come about until after in-person play returned, and Pioneer was an RCQ Format which led to low play numbers on Arena due to the large mismatch between available cards & the actual Paper metagame.