Working age population is decreasing in Europe. It's only really major cities that suffer under development, and even among them it's just some, not the majority.

And despite all the bitching, even extra-EU immigrants are a huge resource for most European countries. In Italy e.g. extra-EU immigrants contribute to 14% of taxes and receive less than 2% of benefits, as many of them come here as young adults and leave before qualifying for pension anyway so the bulk of social services (school and healthcare) is essentially largely subsidized by immigrants.

In Germany extra-EU immigrants are on average net contributors to welfare state too.

Yes, many among them stay poor, don't integrate and tend to fall for minor, petty and some for violent crime.

What you hear little about are the insane dangers of organized crime like Italians and Albanians on the other hand, because they move hundreds of billions and are a drag to the economy in most of Europe.