Osama bin Laden’s fortress was heavily constructed–drone-proofed, it seems, when built in 2005. He avoided land-lines and stayed indoors. This is consistent with the need to evade the US and its technology. In contrast, his compound was very lightly guarded. This is consistent with a high degree of comfort–concerning the possibility of a ground raid.
Of course bin Laden discounted the chance of a US commando raid–anyone would have (in fact, that loud ringing you hear is the sound of the president’s giant brass b**ls clanging together as he does his victory lap). There was no need to post a useless armed contingent whose presence could only draw suspicion. If and when we came it would be via airborne munitions.
What is striking is how completely bin Laden appears to have discounted the possibility of being raided by Pakistani forces. What confidence he had in the fidelity, authority and discretion of his benefactors, whoever they are!
Steve 
Erica Brigid 
KXB 
This is pure conjecture.
Absent detailed facts to the contrary, one could also argue that the light security was a sign of desperation and boldness.
Sometimes when one’s attacked and facing bad odds, one’s best bet is to get just as close to one’s enemy as one can and then fight; that way the enemy’s worries about friendly fire diminish his capabilities.
Absent detailed facts to the contrary, one could argue that Bin Ladin knew that if the Pakistanis ever came for him his goose was cooked, and that with all the rumors of him being in Pakistan, every bodyguard he kept near him dramatically raised the odds of his being discovered.
If he chose to hide in plain sight, I doubt there would have been a better place for him to hide; after all who wants to start asking questions and making allegations in a resort town swarming with retired soldiers. If Pakistans suspected that his digs were somehow connected with the army, as many Americans now do, they’d have generally been loath to ask questions the army wouldn’t want asked, especially close to an army base.
Friends knew a murderer who chose to live among and work alongside many cops while he was on the lam. It worked for many years.