Because it is not, it is probably a rehab project. Which means:
1. There are no tenants. The rent numbers are pro-forma, which means estimates.
2. It is not tenable, you have to re-habitalize it first before you can rent them out.
3. To rehab it, it can cost $5-15K per unit. So your minimum rehab cost is $1M! You can do it in stages, but with vast vacancy, you have to live with big negative cash flow.
4. It will probably take at least a year to rehab, but you have to pay the mortage from day one. That is huge cash outflow for a year.
5. What about if it takes two years to rehab and rent out, can you survive it?
6. There is definitely money to be made after the rehab if the rent numbers are real.
So, in summary, if you do not have at least half a million cash to spend, you cannot take a property this size vacant. It is a big aligator, it could eat the buyer alive.
Also, check the location and neibourhood first.
There are people who specilize in rehabs. They take a junk property, rehab it, tenant it, and then sell for sizeable profit.
Go have a look first, it is an interesting thing for discussion at least.