The mass migration is motivated mostly first by the welfare systems, that somehow is open to migrants from day 1 with more benefits than for natives obviously cause of extreme corruption in the West,(same mad policy that the biden/Kamala adminisration had), and secondly by the outspoken word of the muslim brotherhood, take over of Europe and spreading of their incompatible sharia religion.. (probably out for revenge too in the long run with large offensive jihads planned due to the us/"the wests" brutal middle east wars). yeah there are a few more reasons but those are the 2 major & very problematic ones.
Even if we cut off 100% of means-tested and conditional benefits to migrants, illegal aliens would still be motivated by universal/population benefits like public safety, infrastructure, etc. If you lived in a ruined shithole overrun with gangs and corrupt officials, you'd rather live in a US city with well, relatively fewer gangs and relatively less corrupt officials and less blight. Granted much of that exists right now because we import it, because we've created that incentive and include means-tested and conditional benefits in the handouts.
A country can only exist with borders and borders can only exist if you enforce them.