I haven't watched any of these videos, but to get away with using a copyright poem or other content as part of a video (to be fair use) the video would need to

I haven't watched any of these videos, but to get away with using a copyright poem or other content as part of a video (to be fair use) the video would need to add something enough that they would stand if they didn't include the copyright content (artistic, discussion, criticism, humour etc) - I'm guessing in this case that YouTube has decided the poems are too large a part of the videos (Probably one or more of the poem copyright holders has lodged a copyright violation against some of them) and the content creator isn't added significant value to content owned by others.