He blamed Richard III.
How did Henry Tudor pull off that trick while in exile gathering his small army in Brittany? I would think the reigning monarch would have better control of things in the Tower and Richard’s nephews, both of whom held better claims to Edward IV’s than him, were ostensibly under his protection as regent and then outright king. Henry certainly had a motive and Shakespeare was certainly a Tudor apologist, but that doesn’t automatically exonerate the bent backed fellow in charge.