It's less that Communist States have massive intelligence networks on their own populace because they are Communist, and more that states kinda just do that. American privacy violations are horrifying.
The "difference" largely comes from bourgeois media overplaying the bad elements and underplaying the good elements of Communist projects, while downplaying the bad elements and overplaying the good elements of Capitalist projects.
Combine this with the widespread fact that the US intentionally infiltrates and destabilizes states that even flirt with Socialism in the Global South, with hundreds of assassination attempts on figures like Castro, and it starts to seem more reasonable.