A PDF does not know it contains a table
It contains text at coordinates. The table you can see is an illusion produced by consistent alignment — and sometimes by drawn lines, though plenty of tables have none.
Extractors that look for ruling lines therefore miss most real tables: bank statements, invoices, price lists and reports are routinely laid out with whitespace alone.
This clusters the horizontal positions of every text fragment down the page and keeps the positions that recur on most rows. That recovers the grid from the alignment itself, which is the same signal your eye uses.