I know living by the Saviors has a lot of advantages once you're one of them. Though, is there a reason nobody decides to escape even in the moments they're kind of sentenced to death (see Dwight in The Walking Dead - Hostiles and Calamities S07 E11 2017)?
People have tried
Dwight tried to escape with his wife Sherry and sister-in-law Tina in Season 6, Episode 6 - Always Accountable, after meeting Darryl and Tina being killed by a zombie, they decided to return and take the punishment they knew they would receive.
The iron in Dwight's case. "Marrying" Negan for his wife.
Later in Season 7, Episode 3 - The Cell a man called Gordon escapes, one of the original pre-Negan members of the group it would appear. Dwight was sent to bring him back.
In an attempt to get him to come back Dwight threatened all he loved and threatened to dig up his dead wife.
The man chose death in the end.
This shows that if you escape you know that you will be hunted, and with all settlements in close vicinity loyal (to some extent) to Negan, where would you hide?
If you are found you know that you will be punished.
And even if you are not found you know that your family/friends/loved ones will be punished in your place.
Most people will therefore think the risk of escaping, when weighed up against the relative safety of staying, along with with the various perks that come with being a saviour, is not worth it.