Everyone in Europe has been talking about it for decades and many parties on the left have nuanced views on it, and they're certainly not ignoring it. In the US, "the wall" Trump was banging on about in 2016 already existed. Deportations under Obama were higher than under Trump, and higher still under the Clinton administration.

Secondly in many countries "the left" hasn't really been in power for a long time; often government are in the centre or centre-right.