What is your background? This seems to stem from limited experience. The question should rather be: Why would anyone use the pendular step instead of a shuffle for dodging punches and low kicks? Here are some reasons in favour of shuffle already mentioned, others that are not:
You don't change your stance
With a pendulum step, you change your stance and need ...
In boxing it's common to shuffle back.
On the first step, you plant your back leg into the ground, which gives a good opportunity to send a cross to your opponent, who is probably following you.
It's also common because wider stance gives more stability.
In kickboxing it's also the case if you want to avoid having a narrow stance where both legs can be swept ...
Stability may be an issue. An opponent who robbed your step currently gets a chance to try to sweep your feet or trip you up while your legs are together. Doing the stutter step means they can't get to both legs at once (although there are potential issues with having your weight distributed over a larger distance of one leg gets swept).
Another possibility ...
The reaction time to shuffle step is quicker than the reaction time to pendulum step. If you are trying to avoid being hit in the face by a punch, for example, it's easier to evade by shuffle stepping than pendulum stepping.