From what I've read, the $250 is refundable at the expiry of the visa, provided no breaches (there is a small amount of overstay latitude). I expect the US administration is rather hoping a 10-year visa holder, say of a B1/B2 visa, will have forgotten all about paying the amount in the first place and will never bother to reclaim.

If entering on a B1, the likelihood is also that the $250 will have to be funded by the employer. The chance of the employee being in the same job after that length of time, and then being bothered to claim the reimbursement on behalf of their employer, makes it even more likely that most of those fees will be forfeited having been lost in the midst of time.