I fixed a few things for them but most of it continues to deteriorate as the landlord repairs nothing.

@Jason Wolff Account Closed May happen as Jason alludes to but its very rare.. and with the reality of many inner city dead and dying towns its a real issue.. property is not worth what the tax's are owed so the properties just sit there and gather mold and dust and deteriorate..

They may have lucked in with a couple good tenants at the start, however, their business rapidly deteriorates with one bad tenancy or worse, a devious tenant who knows how to use the landlord-tenant laws to their advantage.

This is my day job, and it's been both horrifying and interesting watching our healthy capital markets gradually deteriorate into a Michael Lewis financial disaster book. 

Older neighborhoods deteriorate, and owners repair/upgrade at various rates along the way.

If things aren’t working then you get it back at year 3 vs 5 and can mitigate deterioration. 

Even if unmodified, the shields/sleeves on the wires have deteriorated with age - or become part of someone's nest - leaving exposed wiring in walls, ceilings and attics ... we had an incident a few years ago where a tenant drove a nail to hang a mirror and shorted out three rooms {new acquisition at the time that has since been rewired}.Additionally, household electrical demands (a few light bulbs, a radio, and {perhaps} an electric icebox and/or range) were far less in the age of K-n-T and installations were not designed to accommodate today's electronic lifestyle.  

Unfortunately, post housing bubble the area has deteriorated, renters have moved in, and my property value has dropped by fifty percent.

Slowly he fell behind on payments, and eventually stopped paying all together as his health deteriorated.

There were 2 fence boards that needed me to secure with screws after they came loose and when I did, I noticed that the backing/supporting 2x4 was pretty deteriorated, but the fence boards went back into place well enough.