Because ``<>'' never does an explicit close, line numbers increase across ARGV files (but see examples under eof()).

The OP seems to want to process multiple files from the command line. The relevant example from the entry for eof is:

   # reset line numbering on each input file
    while (<>) {
        next if /^\s*#/;        # skip comments
        print "$.\t$_";
    } continue {
        close ARGV  if eof;     # Not eof()!
    }
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