Rents are pretty high and I am seeing a lot of people rehabbing in what used to be undesirable neighborhoods.  

A bunch of cities in western WA have been very undesirable and have some of the worst crime stats around, but they are also the fastest rising home values/rents in the country right now. 

Why is it undesirable?

You never know who can bring the undesirable element to your property.

If they regarded it as outdated or undesirable anything is possible.

If they pay prior to be evicted, they have just become an undesired tenant and will get max rent increase until they leave.  

The property is damaged beyond reasonable repair (although you said it's turnkey), the tenant's have not been paying rent at all, the rents aren't actually set at $1,000 per unit, the area is too undesirable even for investors to handle, etc.

Las Vegas ones are 80% undesirable as well.

I could see a 2bd 1 ba but a 3 or 4 bd 1ba sounds very undesirable.

It depends - if I carefully screen tenants, clean up the property and take undesirable behavior seriously in my buildings, I'm likely to improve the whole neighborhood just a little.