a) developers doesn't want to show their faces or wanted to go anonymous, it could be, but they might be hiding on this reasons so that when they run off, no one will know them
b) poor written whitepaper, maybe they are in a hurry to released it and perhaps just hire someone to write for them without checking the output. And then someone will call them about the copy whitepaper
c) the design of their website is poor. Same with whitepaper, this scammers wanted to put up their website ASAP to show that indeed they are real. But if the website UI is poor and not appealing and you think that they are taking about millions but can't even create a good website that it looks like a 10 year old build it, then think again on investing on them.
I do not agree with a. I know of a project that refused to share any information of the team. From their admins to the CEO was keep private, and people were investing. After a long while of maybe almost 2 years, the CEO finally shared the info of who he was. That project was a genuine one yet, you see how that went? For your option c, it isn’t necessarily true because I’ve seen great project with a simplistic website and have also seen scam projects with really amazing design (just to entice you).