It is a simple answer, speculation creates a troubling climate for marketers, and to tell the truth it is not more than a simple monopoly of Rice Mills, since comprise 70% of rice that exist in the country.
It doesn't matter if you missed being specific, don't worry about making mistakes, that's the only way your going to succed and that's the point. Besides you have a whole community to assist you... But if your question was literaly to know why rice is going up in price, it's firs of all weird, for the reason that Colombia has 300,000 tons from this week alone, plus close to 65,000 more tons comming in from the US, and not to mention the other 100,000 tons from neighboring countries. In other words you have enough rice for half a year. So if you remove the obvious the truth of the matter is that a few mills control the product so they dictate the prices because like you said the monopolize the product. Therefor the distortion in high prices! Of course among other factors. But the main one is the manipulation of the market by a few that control it!
I am not an expert in economics, but I would say that a reason could be that world's population is increasing and is globally improving its life compared to the past. The consequence is that more and more people can afford to buy larger quantities of food than before, which causes the increase of the price of rice and other cereals and of foodstuff in general.
Hope it helps!
Your question is grammatically incorrect, it is a fragmented sentence and doesnt really make any sense.
If you want it to be correct you could say
"Why is raising the price of rice a good idea (or a bad idea)?"
Or you could say
"Why raise the price of rice?"
I also think it's because the world's population is raising extremly fast and they have problems with providing enough rice for everyone or they don't have enough areas to cultivate rice in an amount that's sufficient.
you can say "Why is the price of rice raising?" it is gramatically correct, because the question you ment to ask was in Present continious tense.