Why does مُحَمَّدٌ not automatically follow the ghayr munsarif pattern merely because it is a name?

Ghayr Munsarif: Basic Case Pattern and Exceptions

• Because a proper name can never be ghayr munsarif.
• Because proper-name status alone is insufficient; another recognized cause is required.
• Because every Arabic name must take kasrah in all cases.
• Because tanwin always marks a foreign name.