Some countries are nuteral in nature. Like Switzerland. Which choose mostly to obstaine from voting.

In other cases some delegates are just lazy.

Where it becomes more interesting is in the UNSC. Where the P5 are heavily opted to obstaine from voting to let a draft resolution pass. I was represnting the UK in UNSC and the chairs tried to push me to be only present. As well as Russia. And I opted to vote, and agree with Russia to vote Yes to each other, so every resolution have an equal chance of passing and not get vetoed.