TEMPO + TSRAGR
You said '.....so why not have an SOP that reverts to monitored approach on that occasion....???'
This would introduce in effect TWO different type of approach procedures. I prefer one and having operated both BA's 'monitored approach' and other methods in a previous life I find the BA method works well and as has been said is less confusing to operate than to write down and explain!
Don't know about other operators but BA also try and standardise across fleets where possible. It certainly makes conversion courses a little less stressful (I've done three within BA).
There is a lot of misconception about BA SOP's but on the whole I think they are as valid as any others and can only be fairly questioned by those that operate to them.