Why we don't add alif al fariqah to:
1.واو الأصل\ waw al aSl\ the original waw: the reason why we don't add it here, is that in these two examples يدعو or يسمو. the waw is originally in the verb, if we delete the waw the verb is broken and no longer means anything; يدعو becomes يدع which isn't right, يسمو becomes يسم which means a different thing.. etc... while in waw al jama'ah we can remove the waw and the verb maintain solid, e.g: فعلوا without the waw فعل, and خرجوا without the waw is خرج.
2. واو جمع المذكر السالم \waw jama' muthakkar salim\ the plural form of a masculine noun: to explain the difference between واو الجماعة waw al jama'ah and waw jama' muthakkar salim is that waw al jama'ah comes with verbs, and waw (the plural form of a masculine noun) comes with nouns.
* This is one of the most common misspellings among all, people always get confused when to add alif al fariqah, they either add it to everything even to jam'a muthakkar salim (when they shouldn't), or don't add it at all when the should.