Algerian nationalists sabotaged de Gaulle's offer to discredit him. [causal]
Yes, they would discuss "self-determination" with de Gaulle, but their delegates to any talks would have to be Ben Bella and the other four hijacked leaders, still languishing under lock and key in France. It was an adroitly calculated move, designed to provoke rejection by de Gaulle. For the G.P.R.A. recognised that the "self-determination" gambit had won for France more points both in Washington and at the United Nations than anything previously attempted; therefore, de Gaulle's initiative could not be allowed to prosper, and he himself must be made to appear culpable for torpedoing it.
XREF: Strategic provocation to force an opponent's self-damaging move echoes Cold War diplomacy and decolonization tactics elsewhere.
Horne, Alistair, A Savage War of Peace- Alge…, loc. 1170