My old worlds aren’t updated with new villages or biomes

When the app was updated my old worlds where I have a lot of progress haven’t updated with some of the new features e.g. the new improved villages and pillager outposts and the new biome types. I was wondering is there a way to fix that as I can assume that most players don’t want to have to scrap there progress in old worlds just to create a new world where yes they get all the updates but have to start from scratch again and most likely delete there old world as it’s ‘outdated’.

Not sure if that’s a bug but might as well see if it can be fixed or not 

cheers