They do accrue interest, and non-payment IS a fact that could be used against him in other ongoing litigation (since continued non-payment could be added his to profile to indicate intent). His super pac is paying those fees, but the point is it's not hurting trumps wallet directly or immediately. His pacs are running out of money, and as since trump has already exhausted the cults supply of low dollar donors, and the rich folk aren't currently putting money into trump: it'll him later rather than sooner, but yeah... not him paying for anything.