Utilizing past games allows content creators so much freedom and a little less work, which makes for us having a lot more stuff, since so many concepts have already been included in past Sims installments. I will just never get tired of conversions. There was actually a whole Sims game specifically for this era, and much of that content has been converted over to The Sims 4 for us to use.
The Middle Ages are not a new concept to The Sims, believe it or not.