It’s no accident.
You might just think it’s bad luck—you just happened to have ended up with toxic partners. If, once, you’re unlucky enough to meet a toxic person, spend a short while in an unsatisfactory relationship, and then extricate yourself, you might just have had a one-off bad experience.
However, if you continue to stay in a long-term relationship with a toxic person or you have had a stream of toxic partners, you may need to accept that you are choosing this type of person on an unconscious level (they’ll also be choosing you, similarly).
You may be recreating patterns from your past.