I think you will struggle to find numbers that support a high degree of illegal immigration from the US to the EU, and retaliation, justified or not, is the much simpler explanation. For unwanted but legal immigration, this has no impact.

According to that Wikipedia page, this looks very similar to the ESTA.

Having had to apply for that last year, it's not at all clear to me how that could help prevent any kind of illegal or unwanted migration. It's not rocket science to say that "yeah, you're only visiting for a few days and that yes, you intend to go back".

So I think it absolutely is a political circus, aka retaliation.

Just like during COVID, when at one point cases started taking off in France again, some country (can't remember which, might have been the UK) started asking for a negative test before entering. Wouldn't you know it, the next day it became mandatory for people coming in the other way. Cases hadn't moved in that other country.

Retaliation is basically the default for visas. The data obtained from the ETIAS is no better than what they get from the airlines (APN) or scanning passports at the border.