WARNING: The following contains spoilers for Marvel's Avengers, available now on PlayStation 4, Xbox One, Google Stadia and PC.
The decision by developer Crystal Dynamics for Marvel's Avengers to focus on the core Marvel Cinematic Universe heroes, with Kamala Khan as a point-of-view character, left some classic team members on the sidelines. Some, like both Hawkeyes, will be added as the game is updated. But one founding Avenger, Hank Pym, is a non-playable faction leader. He was still known as Ant-Man in the game before a run-in with AIM made any attempt at shrinking fatal for him.
When the game picks up five years after A-Day, Pym runs the Inhuman Resistance from the appropriately named Ant Hill in the Utah Badlands. Players first encounter Pym and the base in the campaign, when Hulk and Ms. Marvel are the only playable characters. The base can be returned to as a hub for daily faction quests, where Pym will acknowledge every Avenger's presence when they take a mission -- well, except for one: Captain America.
Captain America is missing and presumed dead after the disaster at the beginning of the game. After he's found and re-joins the Avengers, you have free rein to play as Cap in the finale and post-campaign content. However, if you take Captain America to the Ant Hill, there's no contact with Pym. Pym remains in his usual spot at the Ant Hill, where he's non-interactable. Pym will occasionally have a few lines of dialogue if you take a character up to him, but he seems to have nothing to say to the Star-Spangled Avenger.
It's a glaring omission given the iconic relationship Captain America and Ant-Man have had throughout comics history. Pym and the rest of the Avengers were the first people to encounter Cap after a Namor tantrum freed him from the icy tomb he'd been trapped in since World War II. Pym, then known as Giant-Man, was the Avenger who rescued Cap from the icy waters that day. A brief skirmish between Cap and the team includes him squaring off with Pym. After claiming that he'd fought larger opponents back in his day, he uses judo to take the big man down. Ultimately, Pym's partner, the Wasp, is able to calm Cap down and end the skirmish.
After years as teammates, Cap played an essential role in Pym's darkest hour. After Pym attacked a defenseless opponent, Cap made the decision to suspend him for his erratic behavior, pending the results of a court-martial. Pym suffered a mental breakdown as a result. That led to the infamous moment when he accidentally struck the Wasp, which saw his marriage end and Avengers membership revoked.
Pym would eventually return to the Avengers after redeeming himself. In a reversal of fortunes, Pym would play a key role in one of Cap's low points, in the infamous "Streets of Poison" story arc. Exposure to the street drug Ice caused it to bond with the Super Soldier Serum in Cap's blood. The result turned him into a maniac. After the Black Widow and Diamondback incapacitated Cap, Pym removed his tainted blood. His work to uncouple Ice from the Super Soldier Serum proves to be moot, as Cap chooses to go on without a performance-enhancing drug in his system, but he still saved Cap from being the Marvel Universe's poster child for roid rage.
Cap and Pym's relationship carries over to other universes as well, though it's often less cordial. Mark Millar and Brian Hitch's Ultimates turned the more unsavory aspects of the classic Avengers up to 11, including Pym's domestic violence incident with the Wasp. Ultimate Cap eventually takes it upon himself to teach Pym a lesson. That led to a brutal fight, which Cap won. Pym would be expelled from the Ultimates in its aftermath.
As for Marvel's Avengers, Pym's lack of reaction to Cap could be anything from a glitch to an oversight. Given how often the game will be updated, dialogue or even further missions involving Pym may be patched in down the line, which may correct Pym's snub of the Sentinel of Liberty.