Too much controversy over sensitive trails in the area. There are only three official trails. BKB, Yog Pots and Summer Lightning. All the rest, including Telegraph, are unofficial and generally natural unmaintained or unofficially maintained trails.
Pitch and Holmbury existing trails are generally fine under the Hurtwood management, but outside of Hurtwood there's a fair bit of sensitivity. Many are tolerated but as they become popular or advertised a lot the locals and/or landowners start ranting. The press also like to pick up on this siding against us "drunken swearing hooligans" (as we were called in one local newspaper) and "vandals" (again in local and even national news recently, thanks to a certain ranger).
It's tempting to tell the world about all the trails, but the way things are going, we'll lose the lot and have armies of influential ramblers on the warpath. It's better to keep it as it is where the tourists can do the signature trails and anyone who wants more just explores or goes with people who know. It keeps the bulk of the traffic around the maintained areas also.
P.S. A little secret on trails - Strava (specifically segments). I'm in two minds whether it's a good thing or not though.
Anyway, all that said, Surrey Hills is about the best area for MTB in the south of England in my opinion.