is because Hezbollah didn't get everything it wanted.
Yes, as was widely reported in late May, after a week of street fighting where Hezbollah routed pro-government militias: Hezbollah scored big in the cease fire talks in Doha.
Despite being a minority in the proposed governing coalition with the majority March 14 Coalition, Hezbollah won veto power over cabinet decisions and got the government to back off the demand that Hezbollah dismantle its independent telecom system.
However, something else happened after Doha: The new governing coalition re-appointed the Sunni March 14th-Coalition's pick for prime minister, Fouad Siniora. (Hezbollah boycotted the governing coalition 18 months ago when Siniora was appointed the first time by the majority March 14th Coalition. The Hezbollah boycott is what eventually what led to the street fighting.)
Hezbollah's aspirations for power are at odds with the political facts on the ground, which demands compromise and coalition.
The fighting will continue.