I hope you are genuinely asking this question, not because you are sour that you didn’t get the visa to go abroad OR you just want to divide the country (further) into two groups.
If yes, then I will engage myself in this discussion.

Before you ask us why we want this, let me ask you why you are against it? Do you fear that we will take over your jobs? Are you afraid that people here are more qualified? Let me break it to you, many of the folks in Nepal are equally qualified, if not more, and nobody needs to be afraid of this small group of NRNs.
One of the legit fear has been stemming from Indians who could take citizenship of Nepal, but last I checked, India only allows OCI which is not exactly a dual-citizenship. Same with China; so what exactly is the problem here?

Now, to answer your question about why I like Dual citizenship, I want a legitimate and easier way of dealing with everything immigration. The only reason I am not a citizen of USA is because I don’t want to give up my citizenship of Nepal, I am well aware that many Nepalis currently hold both Nepal and second country (US, UK) citizenship; that’s illegal and I don’t support that. To me getting the dual citizenship is just a natural course of preference; it is easier for me to do everything. I don’t want your government position; I sure as heck don’t want to participate in your politics of dhunga-muda. But it will help not just my travel to Nepal easier but with US passport, my travel to any other country in the world is much easier.

Hope that answers your question.