Unfortunately healthcare professionals tend to hope for the best when offering a procedure because although they know that there is a chance something can go wrong, a lot of the time it doesn't, so they often expect the best outcome for everybody in hope! It is impossible for every 'potential' side effect to be listed and if incontinence isn't well researched or a high statistic, it might not get a mention. Also in an emergency (such as cord wrapped around baby's throat), there isn't much time to think about your options, it's all about getting out a live baby ASAP.
For some reason the policy seems to be assisted delivery first (forceps really does seem barbaric in this modern day though!), and c-section as the very last resort, although a c-section can have the reputation for potential bladder damage/incontinence too, so not entirely risk free either.
Having said all that, I had a forceps delivery which caused SPD afterwards for 2 years. While I had Physio for the pelvic agony (felt kicked by a horse every time I stood up), I also mentioned an episode of faecal incontinence I'd experienced 3 days after giving birth.
I was given exercises a it like pelvic floor exercises, where the Physio said "imagine you're trying to pick up and hold on to a pea with your anal sphincter" .... Sounds daft, but it helped regain lost strength.
It was a slow recovery though, and although I wasn't incontinent again it certainly felt like I would be and I didn't dare stray too far from a toilet, always answering the call of nature ASAP!
Time is a great healer though, and it was coincidentally around the 2 year mark that I felt I could 'hold on' a bit longer (never to the point I could pre-forceps, but definitely much better), and the SPD pain significantly reduced. Now all I am left with is a dull heavy ache on my pubic bone if I stand too long or push a heavy supermarket trolley round a corner.
If someone had told me way back in the beginning that it might take 2 years to feel more normal I'd have had mixed feelings; relief that it might not last forever after all, and despondency that the journey is a long recovery. What makes it easier is that it's not bad right up until 2 years when it switches back to normal, it's a gradual improvement and strengthening of the body, so the symptoms get easier to bear along the way as they're not so intense and troublesome.
Good luck for a speedy recovery 