It wasn't by a large margin - the swing states were a lot closer than people think. Its just that the shift nationally was a pretty uniform making the results in the overall electoral college look less close than each state was. Each swing state was within 1-3%, so small differences to splitting or not filling out the ballot mattered way more here leading to split results

The swing states actually moved less to the right compared to 2020 than the rest of the country in 2024. Probably because of more campaigning in those states

EDIT: Also for an example with some specific numbers, let's look at the Wisconsin

President race

Trump - 1,697,626

Harris - 1,668,229

Third Party - 30,015

Senate

Baldwin (D) - 1,672,777 [ 4,548 fewer votes than Harris ]

Hovde (R) - 1,643,996 [ 24,233 fewer votes than Trump ]

If we assume no split ticking, that would mean ~1.4% of Trump voters and ~0.2% of Harris voters in Wisconsin likely left the down ballot blank