Because Trump is in power — so this is a leverage point while law enforcement supports these activities rather than looming over them in a threatening/escalatory posture. In contrast, when Trump was going out of power, J6 happened.
People with nothing or a lot less to lose tend to behave very differently than people with something to protect — a human behavior frequently exploited by authoritarian forces.
It is always easier for the people whose political and economic interests are represented by the government in power to engage in peaceful protest and to leverage their political standing for good and ill.
People out of power tend to meet resistance in peaceful protest, which in turn empowers the more radical voices of protest toward escalation and violence, which in turn creates a lot of space for more violent actors to take advantage and in turn leads to more forceful response etc.
I tend to agree that violence of George Floyd protests tended to be understated but that happened as a reflex to all protests being painted as violent and overstatement of the extent of some of the violence. But a portion of the violence of the Floyd protests was instigated or inflamed by counter protesters and anarchic/criminal actors exploiting the situation. Unfortunately, there were too many people on both sides who waded into those protests looking for a fight, eager to light a match in a powder keg.
A LOT of the people who defaced property and other violent actors were liberal protesters for sure, but far from all. And even the most violent events were far more contained than conservatives continue to pretend. Seattle was not occupied but a large park and surrounding blocks were. No American city was burned to the ground or even close to it. Even a drum fire in an urban protest makes for startling imagery but that is still isolated.
And there were some cases that were astonishing, like the police station siege in Seattle. That was not a city-wide incident and not unlike some far right sieges of federal property in protests in more rural settings.