It's hard to read the motives of other people, especially those we don't know, have never met, but there seems to be two broad categories of people who might give that advice. The first are those who really don't feel comfortable themselves with an investment that many people consider to be speculation, so they advise everyone else to avoid such investments. Some of these people are truly frightened about this, and their automatic response is negative. They mean no ill will, but this is not the kind of investment they would consider for themselves, and thus, they advise all others against it. And to be honest, I hear from various sources that there really has never been an investment quitie like this one, which tells us that anything could happen, so it may be wise adivise to avoid buying dinar. Of course, I don't believe that, myself, which is why I have a substantial amount of money tied up in my own dinar.
The other kind of people who might do this are those who may simply want to keep others away from a once-in-a-lifetime chance. They are not interested in others doing what they are afraid to do, or perhaps have risked more than they should have in dinar, and they think it's ok for them to take this chance, but not ok for others to do so because they want to protect them. And the reasons they may think this are too numerous to count. However, to them this is simply a risky venture, right down there with buying a very expensive lottery ticket, and they know the almost non-existent chances of winning substantially from one of those. The two are not the same at all, but that is how they see it.
Then there are others whose motives I can't discern. There are lots of advisors; ergo, lots of motives. But as I looked at the two major kinds of people I saw who might do this, I realized that they basically have much in common. Some of them are acting like a very protective parent and want to spare their "child" disappointment if it doesn't work out. And others are afraid themselves, and they don't want you to win if they are afraid to even try. So to your question, there are really too many reasons--in fact, as many reasons as there are people.