I'd say that despite his initial lack of motivation to fight after the Cell Games, Vegeta's drive was reignited by Gohan's remarkable strength. Gohan, significantly more powerful than Vegeta at that point, imo served as an unintentional benchmark for Vegeta's own aspirations. Even before Goku announced his participation in the tournament, Vegeta had shown willing to compete knowing Gohan would be there. This suggests that Gohan's prowess played a big role in sustaining Vegeta's rigorous training regimen. Vegeta's inherent nature as a warrior, coupled with that, just kept fueled his hard dedication to training, though likely not in a almost mad insane way like to the androids battle. However, it's likely that without the presence of both Goku and Gohan, were the latter to die as well for example, Vegeta's motivation probably would have dwindled significantly as well as his gains alongside the years, and his training would have become imo more of a means to stave off boredom and internal turmoil, rather than a pursuit of a clearly defined goal.
