Why did Benjen take the black?

[Buried Treasure]

Yes, Manderly held back from acting earlier in ADwD until his remaining son had been returned to White Harbor. But I think the greater point is that Bran would not under normal circumstances have been granted one of the great Houses held by the powerful families. I think when Ned spoke of Bran being granted a keep he meant a small keep with little significance - kind of at the landed knight-equivalent level. That would set Bran up as a the founder of a new cadet branch of Stark (god knows they need one), but his new line would not start off as powerful in it's own right, only become to perhaps powerful if it lasts enough centuries.

[Ser Lepus]

Yes, Manderly held back from acting earlier in ADwD until his remaining son had been returned to White Harbor. But I think the greater point is that Bran would not under normal circumstances have been granted one of the great Houses held by the powerful families. I think when Ned spoke of Bran being granted a keep he meant a small keep with little significance - kind of at the landed knight-equivalent level. That would set Bran up as a the founder of a new cadet branch of Stark (god knows they need one), but his new line would not start off as powerful in it's own right, only become to perhaps powerful if it lasts enough centuries.

It seems the cadet branches of Great Houses tend to be pushed down unless they manage to grab a good marriage that provide them with lands and titles of their own. The cadet branches of the Arryns are merchants or poor landless knights, the Lannisters of Lannisport are pretty much the same...etc. Tywin and Mace Tyrell tried to give lands to their nephews and youngers sons, but only if those were lands conquered to enemies, not divisions of their ancestral fiefdoms.

I think that cadet branches have to pursue their own fortunes once they are removed enough from the main branch that they are considered barely distant relatives. Many younger sons probably join the Faith or the Citadel if they can`t find a rich wife.