Why is it some signal failures seem to shut the line down. I was on
the Circle line yesterday when there was a signal failure at High
Street Kensington and the service was suspended. Is this because the
signal affected was for the junction so trains were not allowed to go
past it ?

I thought if the signal was stuck on red the driver was allowed to go
past it but are there special rules at junctions. If that is so would
it not be better to describe it as a points failure which to me makes
more sense why the service is suspended.