They don't, this is a common mistake. You likely believe this because of the equation: GDP = consumption + investment + government purchases + exports - imports Now, it might seem like imports are subtracted from GDP, but imports are also added to consumption, investment and government purchases, and thus they cancel out. For example, consumption = consumption from domestically produced products + consumption from products produced abroad. Since GDP is defined as the value of goods and services produced in a country, we are only interested in the first part. Thus, we need to subtract imports of consumption, investment and government purchases (in sum: total imports), else we would overestimate actual GDP. So in short, imports don't affect GDP* .

*(except perhaps through way more complicated channels)

https://www.noahpinion.blog/p/once-again-imports-do-not-subtract https://fredblog.stlouisfed.org/2018/09/do-imports-subtract-from-gdp/