The difference is that it doesn’t need everyone to agree on one thing to make changes. “Boycott coke” requires a substantial mass to boycott one specific company. Demanding change from politics is much more broad and targets whole industries instead of specific things. Like bans on single use plastic, or pushes for EVs.

Apart from that, you most often have to create alternatives before people can abandon bad products. Could everyone stop using cars? Sure. Will it happen? No. But if we start to expand railway through politics, will more people abandon their car then cause they get around by train much more efficiently? Way more likely than without it.

I recommend Kurzgesagts video on the topic whether we can stop climate change. It goes exactly into this.