Comment by jvolkman

The process is somewhat archaic (often involving mailing around paper checks) and I imagine many people just don't want to deal. Rolling over pulls your money out of the market which means you could miss a good day (or a bad day).

I left a trail of 3-4 accounts until just recently, when I rolled them all over to my current Vanguard 401k. They were all invested in the same Vanguard fund so there's not much change other than simplicity.