ELI5: Why do so many English and Massachusetts town and city names end is -sex

I know that Massachusetts gets its naming scheme from England, but why do they end with that and other things.

Gloucester and Manchester end in -cester

Essex, Middlesex, Sussex all end in -sex

Salisbury and Newbury and in -bury

Hampton, Nortons and Suttons end in -tons

Framigham and Whenham end in -ham

Cambridge ends with bridge