“You are not the customer, you are the product” is true so often, but in many cases (like this one) it doesn’t really apply.
First off, “not the customer but the product” is an inherently antagonistic relationship. Your goals are opposed to Facebook’s, for instance, because you want to spend less time on the platform and you want to interact with friends and not brands, but Facebook wants the opposite of both. But with HSA administration, your goals and your employer’s goals are aligned: you both want someone who will quickly and painlessly manage your account without being a pain.
Second, “not the customer but the product” implies an undisclosed, extractive payment occurring behind the scenes. TikTok is harvesting a great deal of data from you and selling it to other companies. You are the product in that your data has value. But with HSA administration, the product is just the management of your HSA money; there’s no under-the-table dealing going on here (or there shouldn’t be); they’re getting paid by your company for their services.
Third, “not the customer but the product” relationships are entirely one-way; you have no way to impact the providing company beyond just not using their services. They do not, will not, and at some level can never care about your experience beyond making it as minimally useful to you to keep you on the platform. But that HSA provider desperately needs your company’s business, so if enough of your coworkers raise a stink and get your company to complain, they will make a change.
In actuality, “not the customer but the product” ignores the unfortunate reality of most HR/payroll service companies in this case: they’re just the lowest bidder, contracted at the bottom dollar to provide the cheapest services possible, because your employers don’t have to use their services and don’t care about your experience.
This was a plot point in the recent Flash movie.