Parting Out Properties?

[Brooks F.]

In my area, I'm noticing some interesting things. Large land plots are selling quickly and for good money.

Then I occasionally run across houses with large land plots, which are going for less than the value of the land alone. 

I've been watching this happen, and then I found a seller who is desperate to move, and they are willing to make a deal, especially because I can buy it cash.  The property is split up into 4 lots. The house is on 1, a 2nd house (servants quarters) is on a second lot with frontage, and the other two are land. In fact the other lots already even have separate addresses legally, and have their own frontage. 

It seems pretty simple to me that I could buy the house, then resell the house with just its one acre plot separate from the large almost 100 acre land plot, and double my money real quickly. Comparable houses to this house are selling for about 75% of the list price while similar size land plots within a couple of miles have sold for 100% of the list price. even after commissions and whatnot, it looks like a 150% ROI is realistic in just a couple of weeks. (or months depending on how long it takes to sell) . The 2nd house would just be icing on the cake even if I sold it for pennies.

It seems so simple, I feel like I must be missing something big or others would have already done it...