Margaret Thatcher accomplished much during her time in office including initiating the reversal of a deep decline that had taken hold in the UK since the 1960s.

On top of the fact there were 2300 mourners of the funeral, many were political leaders, past and present.

From Wiki:

"Queen Elizabeth II led mourners at the funeral.[39] It marked only the second time in the Queen's reign that she attended the funeral of one of her prime ministers, the only other time was for that of Sir Winston Churchill in 1965.[40] Her presence at the funeral was interpreted by some as having elevated "the status [of the funeral] to that of state funeral in all but name""