Because there can only be one conjugated verb (veux) and this verb is not an auxiliary.
A past participle would be used only after auxiliaries "avoir" or "être":
- "j'ai mangé" (compound past, active);
- "le pain était mangé" (imperfect, passive).
"I want to talk" uses "want" as the conjugated verb and "to talk" as the infinitive.
In French, there is a bunch of verbs that can be followed by another verb in infinitive, without a preposition:
- aimer/aimer mieux, aller, compter, croire, daigner, devoir, entendre, espérer, faire, falloir, (s')imaginer, laisser, oser, penser, pouvoir, prétendre, savoir, sembler, sentir, valoir mieux, venir, voir and vouloir