My guess is you’re quoting this? https://www.epa.gov/ghgemissions/sources-greenhouse-gas-emissions

The problem with your statement is fragmentation. Yes, “transportation” is the biggest single CO2 polluter followed by electricity, but there are billions of individual cars and lorries out there, across many different nations and laws, so the marginal effect of any single car is infinitesimal, and too difficult to go after. But things like maritime shipping, aviation, and railroads are monolithic, and transnationally regulated, so much easier to make an impact. Commercial transport also accounts for a way, way larger chunk of the 28% than residential transport.

In terms of most bang for buck, we should be targeting electricity generation and industry, as these are not nearly as fragmented, and easier to directly regulate and enforce regulation. If you immediately outlawed the top 100 corporations on the planet, you’d make a way bigger impact on CO2 than say, every residential house in America giving up their personal automobiles. Commercial lorries pollute far more than residential autos.