Because the number before "seconds" changes. In most cases it would be right. It was programmed such that the number of seconds counted down. It would have involved more work for (almost) no benefit for the programmer to have "seconds" change to "second" whenever the numeral before the word became a '1'.
Raymott is right. Putting in special code just to change some canned text in the special case where the variable is equal to one would be a waste of resources.
MS-DOS famously would declare "x files(s) copied," using the parentheses to indicate that they were aware that the noun had to change in some circumstances.
This inability to distinguish between singular and plural is not uncommon in computing- I guess it saves memory as there's less to look at, making things faster so we gain from spending less time looking at the error. :up: