You remove variables in science

Short term versus long term trends. The short term events come and go without a lasting change. We want to know what the signal from the long term trend is.

Because those all vary a lot over the course of years, so if you keep them in you can't tell how much of the change of global temperatures is going to stick around for decades or millennia. That persistent change is called "global warming".

Back in the early 2010s people were saying global warming is fake because global temperatures hadn't gone up significantly in 15 years. This was the case because all those effects happened to result in temporary cooling. They were liars, but so would we be if we pretended El Niño was global warming.