Jarek 🚲
OpenStreetMap generally uses British English, and consequently uses "suburb" in the British meaning, which doesn't require that the suburb be its own municipality. Check https://wiki.openstreetmap.org/wiki/Tag:place=suburb :

"Use place=suburb to identify a major area in a place=town or place=city with a distinct and recognised local name and identity. Suburbs may have uncertain boundaries, may overlap with other suburbs, and are often best mapped using a node"

"OSM's usage of 'suburb' is different than that used by North American English"