it’s actually a major plot point in pride and prejudice that mr darcy doesnt try harder to convince lizzy to accept his proposal but rather his decision to change his perspective and behavior in light of her rejection made him actually attractive to her so that she was more willing to accept him the second time. he specifically tried to conceal his involvement in saving lydia so that lizzy wouldn’t feel obligated to him and only hoped that his helping bingley get back together with jane might bring him into regular contact with lizzy again so that she might see that he’s changed.
he very famously told her in the dialogue preceding his second proposal that he couldn’t bring himself to hope she’d ever change her mind about him and would never mention his feelings for her again if she told him not to
