Because they are typically more affordable and the value add is in creating the second unit or turning it into a duplex (or SFR + ADU). 

I have zero retirement savings and am eager to start building a passive-income portfolio so I am not a burden to my child.One of my biggest hurdles is that I need to boost my income so that in the bank's eyes I can afford the mortgage payment BEFORE collecting any rent.

Seller is willing to owner finance but cannot afford the additional monthly income (the monthly payments would make her ineligible for the HUD senior housing) I'm trying to avoid a typical all cash deal.

If you have low interest debt and can still afford to invest that is ok as long as you have enough cash reserves in case something goes wrong.

(I don't need immediate cash flow and care more about total long term returns).Relatively affordable compared to other large cities (though the same is true for  SFHs). 

I don't see any reason why the Landlord should be responsible for health practices of their tenants, but you need to decide for yourself how you want to operate your business.Check out Stessa.

This is creating a lot of opportunity for us by putting skilled workers into the labor force who otherwise would have never left their cushy state jobs.As for other perks....We aren't at the level of being able to offer health insurance unfortunately.   

To get the low down payment, you should look into how you could afford it without a co-borrower. 

You also have to research the health of the HOA as the special assessments can kill your cash flow pretty quickly.

You can still find a good amount of affordable homes!