Explain why plant species alien to local ecosystems grow, as a rule, in disturbed places: roadsides, landfills, river banks

Explain why plant species alien to local ecosystems grow, as a rule, in disturbed places: roadsides, landfills, river banks, abandoned construction sites, dumps of soil, sometimes animals, in grazing and hay meadows, in agrocenoses, etc. Why can’t you find them in undisturbed communities?

“Aliens”, as a rule, are less adapted to local conditions than species living for a long time and co-evolving here. Therefore, the latter are more competitively strong. In disturbed communities, the competitive power of local species is weakened by external forces, or these species are simply destroyed. This allows “aliens” to settle in such places.