(sincerely apologize from now because I could sound ignorant here)
I've developed an interest in British Tudor history and even co-run a social media account regarding the same topic. I know that political differences were a reason on why Elizabeth and Mary Tudor didn't really get along. I know both Marys are Catholic while Elizabeth was Protestant. I know that Mary Stuart has a claim to the English throne and married Lord Darnley to further strengthen her claim.
My question is: since Mary Stuart seems as a better candidate in Mary Tudor's eyes (and in my level of knowledge; ps I'm not even 18), why wasn't it written in Mary Tudor's will that Mary Stuart is next in line of succession? Was it because of Mary being in a different country (France) that already planned to claim England as their own with the use of matrimony? Was it because Mary Stuart isn't really the best candidate for certain reasons I don't know of? Or is there not a specific answer from history?
Would appreciate everyone's input no matter what it is.
No need to apologize, but there are a few items to consider in terms of chronology here.
First, Mary Tudor (MT) died in 1558, and Mary Stewart (MS) married Lord Darnley in 1565, seven years after Elizabeth succeeded to the throne. MS's marriage certainly strengthened her claim to the English throne, but with Elizabeth well entrenched, her only chance to succeed would have been at the death of Elizabeth.
The first reason why MS did not succeed MT was because of her foreignness. The English could hardly stand the idea of a Scottish monarch succeeded to the English throne. MS was far worse, in that she had lived most of her adult life in France, and was married to the French Dauphin by the time MT died. To allow a Princess of France born in Scotland to inherit the English crown was unthinkable to MT or any of the English elite. Even though MS was known to be a devout Catholic, her French connections (and later Queenship) and her Scottish birth, made her an extremely unattractive option.
The second major reason was that during the reign of MT, Elizabeth worked to gain followers and allies among the English elite. MT inherited the throne at 38, and despite her quick marriage to Philip of Spain, a child never seemed likely. MT had two false pregnancies, and during the first one, Elizabeth was given more free reign about England. Elizabeth used her mobility to her advantage to gain support among the English nobility, especially convinced protestants and bureaucrats like William Cecil, later Lord Burghley. The transition from MT to Elizabeth was not as smooth as many of the older histories claim, but Elizabeth was still the most viable option, by blood claim, by the Will of Henry VIII (which is what allowed MT to inherit), and by political strength. Alec Ryrie in his survey of Tudor Britain does an excellent job explaining this transition (The Age of Reformation, 2nd ed. pp. 177-185).