Because the real estate consumer has changed.As you read through industry publications, supply/demand reports, and prognostications from segment industry insiders the one caviot many are reporting is the changing dynamic of today's consumer as their habits relate to real estate.The bulk of renters today are composed of Millenials who have a desire to live a fluid lifestyle where movement and change is easier to incorporate into their lives due in large part because of their frequency in changing jobs.

It just takes dedication and a serious budget to mail with the quantity and frequency necessary to regularly produce enough leads that will lead to deals.

How often should I call a list after the initial contact that did not answer? My first guess was wait a period of 2-3 weeks and then call again. 
Is that too much time in between calls or not enough time? 

I am not sure of the exact frequency, we have a couple buildings on site that they service and they have access to those areas.

Typically if you are younger and making good money with your day job you can argue that asset acquisition is more important than cash flow (buying marginal deals but at higher frequency).

Change your rent frequency.

How many letters did you mail, over what frequency, to how many addresses?

@Stuart Fox is right regarding the low quality of tenants and frequency of turnover costs may negate any Cash Flow benefits you may expect.  

Your future buyers will be hit by that cost and impact their affordability.Check the property's flood frequency.

It would be immensely helpful if anyone could enlighten me on what to expect on the subjects of fire, elevator and water tower inspections (frequency/cost), building maintenance, insurance, property management, etc.I believe 5% each month and a 2-3 month fee for finding tenants, please correct me if im wrong.