system
Given the following post, respond as if you're commenting on Reddit:
human
Why are heavy troopers ineligible for covert operations? (Xcom enemy within)

Sure they're big but why couldn't they pass as a covert operative as easily as assault soldiers?
gpt
The training for long range explosives is very time consuming to get the accuracy XCOM need from its troops, making covert training difficult to accomplish in a mid alien crisis time frame.

Also, the intense physical training required for a trooper to carry the standard issue XCOM LMG as well as fire it accurately from a standing position makes heavies very bulky, which draws more attention than an undercover agent can deal with. Hard to blend into a crowd when you stand 6 inches taller with arms like tree trunks.

Edit: As for why an assault can, is because their training requires them to be quick and have fast reflexes. The difference in assault and heavy is like a forest ranger to a body builder; both need to be muscular, but one requires more agility than the other.