MartiusR: If my assumption is correct, I guess that it could be appealing for people who normally don't play too much or don't even play at all. Surprisingly, it has in common one thing with such things like "car mechanic simulator" or "farm manager" - type of theme/main topic, which, is, well, normal (so no fantasy/sci-fi stuff etc) and appealing to "common people". Plus the type of gameplay, which is not especially challenging.
Lifthrasil: The funny thing is, this kind of simulators is mostly played by people who work in the respective field. Farm simulators are often played by farmers. Bus driving simulators are often player by bus drivers and so on. It's strange that people play in their free time what they do during work anyhow. ... But at least in Germany there was an extensive market research that came to this conclusion. Maybe it isn't so surprising after all. I'm a physicist and I love games with good physics based puzzles and I guess many rocket scientists play Kerbal Space Program.
Does that mean that this game will be mostly played by Jesus himself? ;-)
Now that I think of it - I don't know many other "biographical" games. (I used the quotation marks for I reason, but I don't want to go into it.)