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That is about 65-85 ppm N, which, in my opinion, is just about right for weekly feeding.
I've read that hard-cane dendrobiums need the smallest pot that will accommodate the roots (tight feet). I can't tell for sure, but yours appear to have larger pots than they prefer. It is also quite possible that they are being overfed, as Ray mentioned, which can stimulate vegetative growth over blooming.