Why does a balloon don't burst when pricked with many thumbtacks?

Normally, When you prick a balloon with a needle the hole the pin makes creates a weak point that continues to tear as the pressure inside the balloon attempts to escape. ( I.E. To equalise the pressure inside and outside the balloon )

That is the balloon bursting...

The piece of Scotch Tape, however, holds the area around the pinhole together stopping this tearing and preventing the balloon bursting.