I can tell you *exactly* what any possible mutual fund investments during that time would have been doing for them - losing them 6% per year, like mine did for 4 years = minus 25% of initial investment.
They believed the fraud and hype of their bosses, who were selling their own Enron stock while telling them to keep buying and drinking the Kool-Aid.
I'm glad I never liked that crew or I would've been right in the middle of all of it, like friends and acquaintances were. Ironically, I wound up the same way, but by a different path.
A rational person who is investing retirement money for the long term puts money in a long term strategy and deals with the mark-to-market pain.
Your 401(k) is not intended as a vehicle for daytrading for big short-term gains.