why do you think female girrafes prefer male girrafes with longer necks??

Are you sure they do?

I copied this from Google. The duels to which they refer are those between males in a fight.

Long necks come at a cost. ... Having a long and powerful neck would be an advantage in these duels, and it's been found that males with long necks tend to win, and also that females prefer them. The “necks for sex” idea also helps explain why giraffes have extended their necks so much more than their legs.Jul 7, 2010

Female giraffes do not necessarily "prefer" male giraffes with longer necks in the way that humans have preferences for certain physical traits. However, sexual selection plays a role in this dynamic. Male giraffes have long necks primarily for two reasons: feeding and dominance.

To explain why female giraffes might show a preference for males with longer necks, we have to understand the biological concept of sexual selection. Sexual selection is a mechanism that drives certain characteristics or traits to become more common in a population over time. In many animal species, individuals compete with each other to attract mates.

In the case of giraffes, males with longer necks have a competitive advantage when it comes to feeding. Giraffes use their long necks to reach high foliage, which gives them access to more food resources. This allows them to grow larger and stronger, increasing their chances of survival and reproductive success.

Additionally, male giraffes also use their long necks in dominance displays and fights. They swing their necks like a pendulum, delivering powerful blows to their opponents. Longer necks provide more leverage and striking force, making these displays more impressive and intimidating to other males.

When it comes to mate selection, female giraffes may be more attracted to males with longer necks because they are indicative of better health, strength, and overall genetic fitness. Females may also perceive longer-necked males as more dominant and capable of protecting them and their offspring.

It is important to note that mate choice in animals can be influenced by various factors, including individual preferences, environmental conditions, and social dynamics. So while male giraffes with longer necks may have an advantage in attracting females, it's not the only determining factor in reproductive success.