Check out number 4:

9 facts about HSAs that might surprise your clients - Journal of Accountancy

Yes, you can reimburse yourself for qualified medical expenses from a Health Savings Account (HSA) at any time after you establish the HSA. Qualified medical expenses can include expenses for the taxpayer, their spouse, or a dependent. There is no time limit for reimbursing yourself, so you can accumulate the reimbursable amount until you reach a goal

Maybe your client wants to keep money in the HSA to take advantage of tax free growth of their investments in the account.