Why leave a nice home just sitting empty? Investment strategy?

Curious if there's an investment strategy/advantage to just leaving a home sitting empty? I had neighbors move in, stay for 2 years, then let me know one day that they bought another home they loved and were moving. They haven't done anything with the home. It's just been sitting empty for a year, staged with furniture. No long or short term rental, no sale attempt. They're young, early 30s, and definitely seem to be well versed in real estate investing. They own 5 properties in HCOL/MCOL areas. This home is gorgeous. Value is about $1.2M. Comps are selling in the neighborhood so the demand is there.

Why just leave a home sitting empty for so long? Landscapers take care of it, people drop by on occasion to look things over…but that's it. I'm just curious if there's a strategic investment advantage I just don't have knowledge of.