Why Jesus did not/could not do many miracles there because of their unbelief Matthew 13:58; Mark 6:5?

The “could not” of Mark 6:5 is explained by the “did not” of Matthew 13:58. He chose not to do miracles because of a self-imposed limitation on his miraculous energies (see, in principle, Matt 12:38–39; Luke 1:53; 5:31; John 6:26ff). It is not as though he was restricted externally by the unbelief of his hearers.