The non-disclosure is intended to benefit the party that made a payout. It makes plaintiffs view filing a legal claim as a crapshoot as to amount. Settlement might be insignificant ($10), or huge. Also, settlement amounts that are larger tend to be taken as admissions of wrongdoing, so the payer prefers to keep those settlement amounts secret, as well.
$50,000 is probably lower than the cost of going through trial and winning.