How to control which activity types show up in dropdown when creating new activity
Only activity type that has component = Contact gets listed on the dropdown displayed on the contact summary page -> activities tab.


  Bulk Email also has component = contact, then why it is not shown listed on the dropdown? 


Some activity types are reserved for system usage which has filter value set to 1 in civicrm_option_value table. These activity types are filtered from the dropdown list.

Email/SMS activity type will only be shown in the dropdown if the contact has a valid email/phone value stored in it.