Since the release of War of the Spark, Standard has been defined by two opposing forces:
Mono-Red Aggro and Planeswalker Control decks. It's unclear whether the former gains or loses in the rotation, but the latter is a clear winner with the addition of even more busted 'walkers. Garruk, Cursed Huntsman and Oko, Thief of Crowns will join Teferi, Time Raveler and Nissa, Who Shakes the World as among the most powerful cards in Standard.
The cards I have listed above have more in common than their card type. All of them virtually guarantee a favorable exchange, presupposing they resolve. What I mean by this can be illustrated as follows: let's say you play a Craw Wurm and your opponent Doom Blades it. The entire effect of your card has been nullified by the entire effect of their card, but it's almost impossible to achieve the same sort of result against any of these planeswalkers. Even if you immediately land a removal spell on Nissa, your opponent keeps a 3/3 Vigilance land. The same is true of Garruk's Wolf tokens, Teferi's repulse effect, and Oko's 3/3 Elk.
Meanwhile, it's difficult to play counterspells to get around this lingering value problem because Teferi is so ubiquitous. The matchups between grindy planeswalker decks tend to go long, and odds are good that at some point during the game, a low-loyalty Teferi will stick and counterspells drawn from that point will be dead. The resulting world is one where every answer is a liability, and all participants play as few of them as they can manage.
It is this dynamic that has driven so much of the Standard format for the last six months. Expensive powerful sorceries like Scapeshift, Command the Dreadhorde, and Mass Manipulation have been given their time in the spotlight. If there's no way to trade favorably with the threats, the only option is to go over the top.
Enter Murderous Rider.