Trying to suss out the reason why?

I sincerely doubt King Michael's decision to remove his grandson's title and place in the succession was not made overnight.  I know some are thinking that there are dark forces working within the family to have forced his change.

Let's look at it from another perspective.  Romania is not a monarchy.  It is a republic, born out of the ashes of a brutal Communist regime.  The country suffers from a myriad of economic and social problems.  Corruption remains a serious issue.

King Michael is treated as a former head of state.  He and his family are allowed to use the Elisabetha Palace as their Bucharest residence although the property belongs to the state.   Other properties, including Sinaia and Savarsin, have been returned to the king, as these were considered private property.

King Michael and Queen Anne live for most of the year in a modest home in Switzerland.  Crown Princess Margarita and her husband, Prince Radu, live full time in Romania, and have a public role that they have created.  Elected officials dine at their home.  

Romanian prime minister Victor Ponta, a member of the Social Democrats, said he would offer a referendum on the monarchy after the last presidential election.  He was defeated, and the new president is Klaus Iohannis, an ethnic German-Romanian, who has dined with the royal family at the Elisabeta Palace.   In November 2014, as president-elect, Iohannis had a private lunch with the King, and invited him to his investiture.  

Despite this social call,  President Iohannis has made no commitment to a discussion of a referendum on Romania's political system.

Nicholas, 30, was named as a prince in 2010.  He has spent the last five years in Romania, largely fluent in the language, working with NGOS,  taking an active interest in the country and its people.

He recently biked across  the country to raise money and awareness for children's issues.  http://royalmusingsblogspotcom.blogspot.com/2015/03/prince-nicholas-of-romania-to-bike.html

Perhaps King Michael and Crown Princess Margarita accepted that Romania's monarchical status is in the past, and why give this burden to Nicholas, who will never be king.  Why not allow him to have a largely normal life, as the grandson of a much loved and respected sovereign.

This announcement  was unexpected although Crown Princess Margarita and Prince Radu recently traveled Switzerland to see her family.

Nicholas is not being punished.   His plans have not been formalized, but one report says he will be leaving Romania.  

Apart from the official statement this morning, and a comment to the Romanian media by a spokesman for the family,  there are no other reports on why.  We can speculate. 

Nicholas may have decided that he wanted to have his own life back.  Or, perhaps, there was a family recognition that realized that in the years to come,  the family might not have the same "official" support that they have now.  Margarita is the daughter of King Michael, and thus, a Romanian princess by birth.

Nicholas was not born to be royal.  He had not grown up with the expectation of having the mantle of monarchy thrust upon his shoulders.  I have met Nicholas several times, a nice, personable young man, who was dedicated to his family and Romania.  He was popular and eager to promote the country.   But he is 30 years old, and he has not had a full time, remunerative job.  It is difficult to be a prince without an income, especially if he ever expected to marry and have a family.  How would he support them, and maintain even a minimal royal lifestyle.

It could be a lot of things.  A romance.  Getting involved with Romania's fractious politicos (never good for a royal). There are even rumors that Nicholas is gay, but coming out would not be a reason to remove one's title and succession rights.

But I do not think that that anything egregious has been done.   I will be very surprised if this were the case.