A phone line from before WWII works fine to make a call but absolutely sucks for DSL.
And in London many buildings are declared as historic making it hard to get a permit for any work. The best chance is to wait until old pipes bursts and digging has to be done in any case to put fiber along the pipes.
It's not that, it's the building owners (freeholders) refusing permission, or not replying. It's a massive issue.
You'll notice buildings in central London that are listed _but_ have housing association ownership nearly all have fibre to each apartment, as they did portfolio wide deals with hyperoptic etc.
And pipes don't help. Openreach (who owns the copper network) are not allowed in 99% of cases to "fix" copper with fibre under the agreements they have with building owners, they can only make like for like repairs.
The worst affected apartment buildings are 90s and pre 2015ish. Everything after that got fibre installed at build time.
Btw it is worth checking if you have an altnet like hyperoptic, community fibre or g network available. The majority do and if you are just checking for openreach or VM broadband it won't show up.