Maybe for a more high capacity state with a better handle on things, but it would be a bad idea for the Syrian government to publically declare such a thing. A huge part of the populace want Assad’s head and are already mad that the government isn’t acting more firmly against many former regime personnel. Many have been taking matters into their own hands with revenge killings being very common on the street. Publically saying that he gets life in prison will guaranteed cause riots and they don’t need to be stretched any more thinly. They have a fragile hold on power, relatively small professional forces who are very overstretched and huge numbers of trigger-happy militia everywhere. Outbreaks of violence that the disciplined forces can’t control spiraling out into massacres as militia rush in have been been disastrous not only for the bloody toll on the people but also for their integrity as a state and tanked external relations relative to what they could have been. So, they really don’t need to start optional riots that distract their forces and open them up to being hit with another provacation.

Going this way instead they rather have people celebrating in the streets for basically a few words while Assad himself is safely out of reach at his gamer pad in Moscow. BTW him abandoning the country to keep playing Candy Crush safe under Putin has not done much to endear him to those aligned with him who had stayed behind to face Syria’s hostility, hard to make a martyr image out of that.