Some buy to park money, others do 1031 exchanges or they simply buy them for a tax write-off. 

I am at this writing currently selling a 35 acre tract to a big developer who is converting the local golf course here in Oregon that was zoned Open space.. they have been successful in getting the rezone..

I am writing to explore rental opportunities for a recently renovated property that has been 90% restored following fire damage.

Whoever they are dealing with also dropped the ball and the buyers are full of something-everything was in writing and if they signed off removing the financing clause, they are on the hook to buy. 

You should always protect your position, make sure everything is in writing, and don’t hesitate to explore the full value of your deals by marketing to other buyers.

If you operated a business, even without an LLC, you may potentially be able to write off certain expenses.

Write in detail any last steps (like site cleanup or payment) that need to be completed.

ADUs can significantly enhance your property's value by adding living space that can be used for rental income or as additional living quarters for family members.The increase in value from an ADU can vary widely depending on several factors such as the size, quality, and functionality of the ADU, as well as its integration with the main property.

Quote from @Zachary Deal: One thing to keep in mind if you are doing this is that you are likely to create "functional obsolescence" which could mean you are not able to get a new loan against your property and it can be difficult to resell as well. 

Another issue I see with older homes is the layout and functionality is tough to manipulate even during a full gut.