>as you get a chance you immediately transfer your 401k into a self managed IRA accountAnother reason to do this is that you can buy "anything" in your IRA account, including stock market ETFs, leveraged bond fund ETFs (which can be a nice diversification option since you don't pay the full income tax on the dividends that you otherwise would need to outside of a 401(k)/IRA), anything that your brokerage account has access to.
On the other hand, your typical 401(k) plan only has access to crappy financial products and shitty fund managers. My former employer offered a bare bones 401(k) plan with no employer match. I went through and looked at all ~20 of the funds available. There were 2 passively managed index funds, 17 active managers who had underperformed the market net fees, and 1 who had done decently well, maybe matched the Russell 2000 after fees (it was a mid cap fund). I looked further and found, exactly to my expectations, that every single one of the 17 bad funds were run by inexperienced, most likely young, managers. The one fund that did decently had two guys who had been running it for over a decade.
Not all money managers are bad. Some do actually provide some legitimate values, even after fees. But (a) most of the ones available to you in a 401(k) plan suck really really badly, and (b) even the good ones will break you with fees.
It is probably not that well known, but "The wealthy" combat (b) by negotiating fees that are significantly lower than the starting fee by saying, "I am bringing $N million to your account. What fee can you offer me? I am shopping you vs other banks."