The Templars are a great subject for fiction writers as well as pseudo-historic pop culture writers.
Since they were essentially a secret society who gained great wealth and lands and then were persecuted and wiped out by Phillip the Fair, their story presents all kinds of opportunities for fictional accounts.
I don’t know what the problem is with people who attack the writers of these books as long as they are clearly fiction and meant for entertainment. If they blend in some accurate history with the fiction, so much the better.
The problem is not with the books. We have had historical fiction as a genre forever. The problem is that with the deterioration of education and the cynical marketing by unscrupulous authors, who deliberately blur the boundaries of what is 'clearly fiction."
Too many people no longer can tell the difference between "accurate history" and fiction, and there is a media echo chamber which profits by encouraging ignorance. Recall how many times the author of daVinci Code was interviewed on TV and acted as if his schlock was a genuine hypothesis. Imagine how many people think the Code is real: millions no doubt.