That's definitely one of the reasons; evidence gets worse over time. Memories fade, witnesses die or become unavailable, documents get lost or destroyed, and physical evidence degrades. In this case specifically which is centred around a lot of discovery of emails and text chats, you can imagine that in other 5-10 years a lot of that discovery might become impossible to get and could drastically alter the outcome of the case.

It's also generally considered unfair for someone to have an indefinite threat of being sued or prosecuted hanging over them when their ability to defend themselves gets weaker over time. Limitations discourage strategic delays or using old claims as leverage far into the future. Without limitation periods, old business transactions could be reopened forever, estates could never fully settle, people and businesses would face constant uncertainty.

Ultimately, the courts are just better at resolving current disputes than reconstructing old ones.