Left parties provide educational grants, training so you can climb the career ladder and if you lose your job, they keep you safe from being homeless. How would a migrant fare in a country that has none of this? Right wing parties have an incentive to keep migrants as a perpetual underclass.
All parties offer this. Each country has a safety net and worker funded unemployment insurance. Right wing parties want everyone to be financially stable and employed and people not in welfare for their whole life. Welfare should be cut entirely except for disabled and old people. There is absolutely no reason for it to exist for others. Welfare is also the reason why so many people are not integrated into society. They never speak and have relationships with other people outside of their communities.