It's easy to say in hindsight that the first a/c may not need to have been broken off but the trouble with infringements is their unpredictable nature. Did you know the infringing a/c wasn't going to turn left to appear to further close the distance at any time?
If the infringing a/c had turned left separation would have been further reduced and in these circumstances we are required to try and keep the IFR traffic 5nm away from the unknown. Separation was already less than this.
There's also the fact that it's likely the instruction to break off the approach would have been given a reasonable amount of time before you see anything happen on the radar replay. It's possible the inbound was with the tower adding further time delay whilst radar tell tower what to do and even if not large aircraft in approach configuration do not do anything very quickly.
Better to be safe than explaining your inaction at a later date.