Ummm, there's a strong chance I'm wrong since my memory of this one is pretty hazy, but isn't it the case for MARS?
The same thought always occurs to me -- it's almost a given the lead has at least ONE dead parent. If dramas reflected reality, maybe 90% of asians would be orphans or have only one parent... It's a bit ridiculous.
In some dramas (like Oh My Ghost, which I hate to pan because I loved it, but it's the freshest in my memory), the fact that the character is an orphan is perhaps mentioned once or twice, and it barely adds anything to the plot at all. In cases like that, I feel like they might as well not mention parents at all, so we could just assume they had a relatively normal childhood, instead of adding drama that won't be developed (because the death of one's parents really is heavy material, it should be properly addressed if used!)