Why did Hariri surrender so quickly?
Interesting claims here that Hariri was using human shields from outside Beirut:
"All the offices of the government-backed Future Movement in West Beirut have surrendered and many of the pro-government "fighters," many who were invited to come from northern Lebanon, often without even knowing that they were going to fight, have surrendered to the opposition and the opposition has handed these people and offices over to the Lebanese army. ...
Also it is critical to note that many pro-government forces who fought against the opposition in recent days, were people traveled from extremely impoverished areas like Akkar in northern Lebanon, led by the Future Movement to Beirut which was offering money to impoverished people to fight against opposition forces in Beirut. In certain cases people coming from Akkar weren't even aware prior to arriving in Beirut that they were coming to the capital to fight, thinking that they were coming to Beirut to fill labor positions; these are people who were manipulated by the Future Movement.
Many people from Akkar, in this context, quickly surrendered to opposition forces in West Beirut, declaring on local TV and radio that they weren't aware that they were being led by pro-government forces, mainly the Future Movement, to Beirut to fight the opposition. Also some youths who fought for the opposition forces were led to fight with money, however this is a minority. It's important to recognize that the terrible economic situation in Lebanon is leading people to fight in multiple cases."