Yes, you are not imagining it. Many park benches do have armrests in the middle, and one of the main reasons is to make it hard—or impossible—for someone to stretch out and sleep across the full length. These are often called “anti-sleeping benches,” “hostile architecture,” or “defensive design.
The middle armrest breaks the flat surface into two or more separate seating areas. It doesn’t remove seating for people who want to sit normally, but it stops the bench from being used as a bed. Some cities and private property owners install them in train stations, bus stops, parks, and plazas.
There are also other stated reasons: middle armrests can help people with limited mobility push themselves up, mark personal space, and discourage skateboarding or rough play. But the timing and placement often make the real intent obvious—especially in areas with visible homelessness.
This type of design is controversial. Supporters say it keeps public seating available for everyone and prevents one person from occupying a whole bench. Critics argue it punishes people who have nowhere else to sleep and treats homelessness as a nuisance rather than a social problem.
So yes, those middle armrests are very often there on purpose to stop people from sleeping. Whether that’s good or bad depends on who you ask.