From that quote from the
BBC» :
In March, Labour's South Bank councillor Neil Bendelow said the bridge, which was also inaccessible to wheelchair users, was in a poor condition and an upgrade was required urgently.
Apparently, nothing much was done, the footbridge still being used daily - until over six months later, when this suddenly happened:
A railway footbridge has been closed off indefinitely after an inspection uncovered safety concerns.
So, those 'safety concerns' have been there for at least six months, without any action being taken - until now.