Dems want votes, of course. And, a new captive voting block in addition to blacks means power...whether they vote illegally or Democrats succeed in getting them amnesty.
But, this is also about census count increases. Even if they don't vote, if they are imported into blue areas, then they increase Congressional seat allotment, as they are counted in the census.
Also, they become new union members, so Dem donors make money off of them. New membership in the service industries is more lucrative for unions than protecting blue collar manufacturing jobs held by Americans.
And, Dems make voting easier for illegals with opposition to ID/citizenship requirements and voter registration/harvesting. There is no legitimate reason to do that. And, in some areas, they are trying to let them vote in local elections, like school board elections. Once they are voting, it will be harder to keep them from voting in national elections.
And, I am curious: why are you upset about reduced numbers of illegals? I thought no one was above the law.