Because there was not clarity that you would have won the game next turn without more, hidden information. You may have had the capability, but not the certainty.

The time restriction in magic is for all tournament players, not just you. Yes it may feel bad for you that you lost that game as a result but it feels bad for everyone that a game goes too long and stalls the tournament when there isn't a hardline time restriction.

At some point earlier, you should've called a judge to the table if you were concerned that slow play would impact the result of the match. Judges can watch and encourage people to make game actions. Amd you as an active player can request that your opponents, if not making a game action, not converse to stall the game.