I have thought of hiring a PM, it's just that being new to Airbnb/STR space I have concerns about the volatility in occupancy rates and the unpredictability and seasonality of STR income.

When they actually fall is often entirely unpredictable. 

Not always the case, however the risk profile goes up with smaller sized properties due to the unpredictability of these smaller teams over X amount of years.Time : As you mentioned, performing due diligence per SFH investment takes time.

The point is simply that druggies are unpredictable and anyone dealing with these people should have some sort of protection.

Ive looked into mobile homes also, they tend to depreciate a lot and are unpredictable.

What set him off are the constant groups from Socal CA and unpredictable parties. 

Some renters can be difficult to deal with, and there is the unpredictable violence aspect of some areas too.

At the end of the day most things are a crap shoot, values of anything can be unpredictable-RE stocks, bonds, paintings, antiques-whatever. 

Investing in vacation rentals is a smart decision for savvy investors looking for a financial return that won't be impacted by unpredictable market conditions.

Too much government intervention in rent control, subsidized rent, eviction avoidance, foreclosure moratoriums, federal reserve intervention (which is neither federal nor a reserve but a privately owned bank, owned BY the banks (look it up) and unpredictable policies by the government.