I’d be shocked if most companies are retaining these logs longer than the legally mandated minimum. This kind of information is radioactive from a legal perspective. Slack and Teams even advertise automated deletion as a feature.

Long-duration archives can be used against the company in a lawsuit - whoever's suing you would love to get decades of material to look through to help make their case.

As such, it's a large liability, and most companies retain those sorts of records for the minimum amount of time acceptable by law/regulation/customary expectations.