It could be because you are working on a brand new area every single “Sprint “(or equivalent). That’s not prudent assignment of resources(the manager should know this).

I have worked in companies where ownership is somewhat static(same few folks work on a given area of the product) and things get done within 10% of estimates (a lot of innovation too).

I have also worked in terms where ownership is fluid and “resources” get assigned to tasks. Nothing is now “estimatable”. Your experience is probably in line with the latter.