I read it as sword cultivators taking their techniques to the grave, not because they are against sharing, but because by their nature they walk an extremely high risk path. Sword cultivators that develop deep technique through experience probably die in battle before they can properly raise and pass on everything to a disciple, so even if they do have students and disciples they will only have bits and pieces and will have to develop the techniques themselves rather than be taught. On the other hand, because of the high amount of danger in their way of cultivation, many disciples probably fall in battle, meaning there are even fewer disciples to make their way to seniority and mastery. I imagine that the qi hoarding also doesn't help because subsequent generations of sword cultivators have less qi to work with, making their training and cultivation even more difficult.
Consider A-Ting's master, if he wasn't imprisoned in the Pavilion, he may have kicked the hornet's nest with the Baili clan generations ago. I can believe that his imprisonment forced him to be able to take his disciples and train them since he can't go and do anything else.