How? There were nearly 400 patrons in the club. Not one, apparently, was armed, save for an Afghan Jihadi, Omar Mir Mateen, a newly deceased terrorist. That's how.
Why was no one else armed? Why? Because of a state-inspired and misguided loophole in Florida's concealed carry laws which prohibits "carrying" within premises serving alcohol. This effectively renders patrons defenseless against attacks by Islamic extremists or any other type of violent group.
The state of Florida, like so many other states, has created yet another "gun-free killing zone" - much like the killing-zone places where children congregate during the school year. As Donald Trump has pointed out, the best way to avert large numbers of people killed by evil gunmen, such as this Orlando shooter, Omar Mir Mateen, is to allow good people the means to protect themselves - wherever they are.
I live in No. Carolina which is a "shall issue" concealed carry state. "Shall issue" means the state must show a compelling legal argument to avoid issuing you a permit to arm yourself away from home. Convicted felons, for example, are not allowed to 'carry' in No. Carolina. Unlike Florida, you can legally carry your concealed firearm into a restaurant or bar in my state, but you cannot drink if you do so. This resulted from NC House Bill 937 which became effective in 2013. Gun banners and their naysaying media allies forecast it was going to lead to murder and mayhem. Their unified mantra
was "guns and alcohol don't mix." So, what has happened in the past 3 years since Bill 937 was implemented?
The right to self defense is the most fundamental right of every human being and when the state intrudes and limits the right to self defense it is acting in concert with criminals whom neither recognize gun laws nor your right to defend yourself against THEM. That even applies, on occasion, to states themselves. Need we remind each other of what happened to the Jews of Nazi Germany who were stripped of their guns before the greatest pogrom of all, The Holocaust?
The criminals and the terrorists LOVE gun controls; it makes their "job" easy, and that's especially true wherever a state designates a "gun free (killing) zone." In case you're going to visit Florida, here is a relevant list of state-established killing zones there:
Note: Firearms regulations are uniform throughout Florida, and a carry license is valid everywhere other than in a few specially-defined areas. These specially-defined prohibited areas include:
Any place of nuisance as defined in s. 823.05
Any police, sheriff, or highway patrol station;
Any detention facility, prison, or jail;
Any detention facility, prison, or jail;
Any courtroom, except that nothing in this section would preclude a judge from carrying a concealed weapon or determining who will carry a concealed weapon in his or her courtroom;
Any polling place;
Any meeting of the governing body of a county, public school district, municipality, or special district;
Any meeting of the Legislature or a committee thereof;
Any school,or professional athletic event not related to firearms;
Any elementary or secondary school facility or administration building; If school is in session
Any career center; (Commonly referred to as "Technical Schools")
Any portion of an establishment licensed to dispense alcoholic beverages for consumption on the premises, which portion of the establishment is primarily devoted to such purpose;
Any college or university facility unless the licensee is a registered student, employee, or faculty member of such college or university and the weapon is a stun gun or nonlethal electric weapon or device designed solely for defensive purposes and the weapon does not fire a dart or projectile; (With an exception for students, faculty and visitors keeping firearms stored in their cars.) 
The inside of the passenger terminal and sterile area of any airport, provided that no person shall be prohibited from carrying any legal firearm into the terminal, which firearm is encased for shipment for purposes of checking such firearm as baggage to be lawfully transported on any aircraft; or
Any place where the carrying of firearms is prohibited by federal law.
In Seaports – The seaport must provide clear notice of the prohibition against possession of concealed weapons and other contraband material on the premises of the seaport. Any person in a restricted area who has in his or her possession a concealed weapon, or who operates or has possession or control of a vehicle in or upon which a concealed weapon is placed or stored, commits a misdemeanor of the first degree, punishable as provided in s. 775.082 or s. 775.083.
In the Savannas Preserve State Park – It is unlawful for any person, except a law enforcement or conservation officer, to have in his or her possession any firearm while within the Savannas except when in compliance with regulations established by the Fish and Wildlife Conservation Commission applying to lands within the described boundaries.
Anyone lawfully carrying a firearm in Florida in a concealed manner, may briefly and openly display the firearm to the ordinary sight of another person,
Help stop this PC madness. Go Trump.