Automatic payment removes the risk of a missed due date, which is its purpose. Set at the minimum, it also removes the moment where a household would have decided to pay more.
The minimum is calculated to be small
On a revolving account the minimum is typically a small percentage of the balance plus accrued interest and fees, subject to a floor amount.
Because it is proportional, the required payment falls as the balance falls, which stretches the remaining term rather than shortening it as progress is made.
The structure is not hidden. Card statements are required to show what paying only the minimum implies for the payoff period, and the figure is usually striking.
Automation removes the decision point
A household that pays manually confronts the balance every month and can choose to send more when a month allowed it. Automation replaces that with a default.
Defaults persist. A setting chosen during a tight period continues unchanged through periods when the household could comfortably have paid several times as much.
The account stays current throughout, so nothing in the servicing relationship signals that anything is wrong, and no notice is generated.
Interest charges obscure the lack of progress
When a minimum payment barely exceeds the interest accrued, the balance falls by a small amount each month while the payment leaving the account looks substantial.
Over a year the outflow is large and the balance reduction modest, and the gap between the two is the interest cost of the arrangement.
Reading a statement's payment amount alone gives no sense of that split, which appears only when balances are compared across months.
Installment loans behave differently
A fixed installment loan has a scheduled payment that does retire the balance by the end of the term, so autopay at the scheduled amount is not the same trap.
The equivalent issue there is early-term amortization, where most of each payment covers interest, and additional principal payments have their largest effect early.
Some servicers also offer an interest-only or deferred arrangement, in which the scheduled payment genuinely does not reduce principal at all.
The audit that answers the question
Comparing a balance today against the balance twelve months ago, alongside the total paid over that period, gives the actual rate of progress.
If the difference between those two figures is large, the arrangement is funding interest rather than retiring debt, whatever the payment history looks like.
That comparison takes minutes and is the check most often skipped, precisely because automation was adopted to stop having to look at the account.