They come to realize  fractional ownership in a semi-active project with far less control is not as advantageous and eliminates the ability to build the more personal and meaningful relationships with lenders that comes with going through the more natural progression of growing a portfolio and business. 

Do they pay for vacation pay, medical insurance, workers comp, payroll taxes, PTO & holidays, ongoing training, trucks & commercial vehicle insurance, liability insurance, admins, marketing, SEO, liability insurance, bonding fees, licensing fees?

There was a bill in Congress aiming to extend or modify the bonus depreciation provisions, but no definitive changes have passed yet.

In some states, the taxpayer has the ability to redeem the property for [insert time period] after the tax sale.

Everything revolves around consistently receiving rent and having the ability to increase rents faster than inflation.

Flexibility is the ability you need to embrace. 

Look at the lenders ability to perform and act honestly.

Early closure penality or ability to refinance?

A desire and ability to share their knowledge4.

This costs money, and you are paying for the ability to have a unit turned at any time.