The details were provided in the changeset comment, to which you could have replied.

Sidewalks which do not connect to anything are *not* useful for creating running/walking routes. They're at best decorative and at worst spam.

The sidewalks added by you which connect to other highways are still there, together with sidewalk:$side on the parent highways.

I walk and run a lot in London and have added a lot of crossings and separate sidewalks. These are accurately mapped, actually work for routing and include accessibility features. Even after adding them with the best available aerial and street-side imagery, it's still worth walking the newly-added sidewalks with StreetComplete to add missing details.

Incidentally, in what way is London your local area? It's only just on the same continent.
https://hdyc.neis-one.org/?asturksever