Reason for Ant-Man not appearing in Infinity War
Having watched Ant-Man and the Wasp I cannot see any decent reason why Ant-Man was not included.
In the beginning of Avengers: Infinity War, it's mentioned that Scott took a plea bargain, and this is played out in Ant-Man and the Wasp, 2 years house arrest and 5 years probation.
Without explaining the film entirely, stuff happens but towards the end of the film, he has this heart to heart with his daughter about helping people vs finishing his house arrest and staying clean. The outcome is that he suits up to save the day.
At the end, everyone is fine and there is a montage of people doing stuff, Scott having his tag removed, his friends doing stuff in their office, Scott takes Cassie out for the day. Hurrah happy ending!!
As the post credits scene reveals, this all happened pre-snap of doom. We see a scene where Scott is Ant-Man again, hanging out with the Pyms (which is a violation of his parole) and about to do some more Quantum Realm stuff. Then the Snap happens.
Given that we know there is a clear few days between the end of the action in the film and the finger Click of Doom, I feel there is no good reason for him not to be involved.
Here are 2 reasons I have heard and why I feel they don't stand up:
a) He is on probation and didn't want to be seen publicly. - In the film he has run this risk multiple times and even goes Goliath size to mess with a ferry in the water. I think he would accept the risk given the attacks in New York.
b) The Avengers don't call him and respect his plea deal. - I think the Avengers still watch T.V./The News and would have seen him as Ant-Man and so would've been aware that he happy being Ant-Man. They would have called to say "Hey, I see you still being Ant-Man, we need you if you want to come?" Even if they don't ring him, do you think he would have ignored the attacks in New York mess around on a roof top with a Van Sized Quantum Tunnel?
Has anyone read any other reasons why Ant-Man wasn't in Avengers: Infinity War that still makes sense?
In Infinity War When asked where Hawkeye and Ant Man are, Cap and the team (i think it was Romanoff actually) state that they took a plea deal to see their family, now while this could be seen as the team disagreeing with that decision by the way its reacted to, it more likely that they don't want to cause issues for Barton and Scott's plea deals, that basically ties it up lore wise.
While yes they would be able to see things on TV, this all happens at the same time. all of the celebrating in the ExCon office seems to take place the day after Scott's probation ends, and so does the Cassie trip. so this is only 1 day at most after his freedom, Cassie trip was likely same day, its possible celebration as well. What we don't know is how long after his release the post credit scene takes place. but it is likely a couple of days or more as they had to build a new machine. but remember the rest of the Film only takes place over 2 days
But once the severity of the events in IW is known its possibly only a day or two between the end of A&TW and the Big Click, so that would mean that the events in Edinburgh have already taken place, and from then everything happens so fast in IW that they may have changed their minds but wouldn't have had time to get him to Wakanda, or just they were too busy to think about calling him
Below is potentially a major spoiler for the next Avengers film, do not look at if you don't want it
This is theory at the moment but there are pictures of Ant-Man during the Battle for New York in Avengers Assemble, which means he travels in time through one of the time portals mentioned in the post credit scene. so it seems that AntMan is key to saving the day in the next second part of infinity war, so its probably that the produceers decided to have him not be in the first one means they don't need to risk the whole "having 2 Antmen" as once in sections of IW