I think your confusing IRS reporting requirements with SAR (BSA).
By law you're required to report any financial transaction in cash over 10k. (e.g. if a dude walks into a car dealership and plops down 80k in cash for a Tesla, that's gonna get a form 8300) -- basically this is to stop money laundering by exchanging cash for services/property in kind at the point of sale.
SAR's are more for detecting henky shit going on at a financial institution, usually money laundering, insider trading, terrorist financing etc..). For my neck of the woods, that's more insider trading, but for banks, it can be stuff like depositing 5 grand into a new account (or multiple ones adding up to that much). Basically trying to detect money laundering. It'd be unusual in the old days for a withdrawal to get flagged with an SAR, but since their ass is on the line they tend to overreport these days.