Matching money is 100 percent return in the first year. Why wouldn't you? Some 401ks allow ETF investing. So someone could double their money and then buy BTC ETF.
Discussion
A couple reasons: math, flexbility, and the inability to self-direct.
Yes, there's a 100% return in the first year, and then what? Bitcoin will put out multiple 100% returns over the same several decades.
You're giving up freedom money for locked up money.
Many 401Ks, including mine, are not self-directed, or at least not completely self-directed, meaning you can't treat it as a brokerage IRA. Your options are limited to basket funds, typically labeled "Target 2050" or some such nonsense.
Mine allows 50 percent of the funds to be in a brokerage and IBIT ETF is one of the options.