When you shut off the engine the carburetor is left full of gasoline.
When the unit sits for months gasoline evaporates from the carburetor leaving only the non-volatile parts behind, often in the form of a heavy varnish like gummy gooey layer. It plugs up the tiny passages in the carburetor.
The ounce of prevention to keep this from happening is to empty the carburetor before putting the unit into long term storage. Find the fuel shutoff valve and close it, let the engine run until it has used all the gas that was in the carburetor. Usually takes two or three minutes at idle, less if loaded. Alternately you could siphon all the gas out of the tank and run the engine until it's out of gas.
All gasoline engines are that way. Well, carbureted ones anyway.
Did you follow these instructions in the owner's manual page 14?
and page 18 where they continue with instructions how to clear the jets and oil the piston rings.
Once the carb has got gummed up it needs to be taken apart and cleaned. Squirt "Carb Cleaner" through the passages. Denatured alcohol or acetone works too but be careful of acetone on plastic & rubber parts.
Another possibility is the low oil cutoff switch has stuck. Check oil level , then disconnect the wire and see if it starts. If it does, you need to fix the switch.old jim