They do get reported and they do eventually get sorted; but the lack of any planned vegetation management means that the problem is only going to get worse and more frequent.
There's also the OLE to consider. In a couple of places on the WCML, trees in the ballast in the ten-foot have grown as high as the OLE. That's another problem waiting to happen.
Then there's the forests growing in the structure of our bridges and viaducts.
It is planned. Perhaps not to the standard or intervals that some desire, but it is most certainly planned.
Totally obscured signals do get sorted immediately and encroaching vegetation at signals is resolved as soon as practicable.
I'm not denying here that there's an degree of risk here, as fallen trees have been a factor in serious events. But branches fouling the running lines do get pruned back too.
Wrapped up in changes in working practices through safety and prioritising elsewhere doesn't mean it's any less planned.
That said, I've experienced more damage through fly-tipping and vandalism on the railway than I have through vegetation.
I do however agree that lineside vegetation is observed more and more over the last decade and possibly longer than that.