Why are some monarchs sent to exile after a country is declared a republic?

Your question is flawed.

You start saying that you like monarchy, and then you wonder why countries which rejected it exiled the former monarchs.

Quite the opposite: if a country abandoned monarchy, it is most likely because it wasn't very popular, so it is perfectly natural to treat harshly the former rules.

Actually very often exile can be considered a soft punishment, considering the amount of damage they might have done towards their former country.

Most absolute rulers, be they Monarchs or dictators, will accept no diminution of their power, so that when the populous approach them with such a suggestion they, the absolute ruler, relinquish some or all of their power,they tend to reject the demands of the populous.

If the feelings of the populous are strong enough then the populous will persist with their demands, and typically, the ruler persists in their rejection, and thus tension in the country builds. That tension often reaches a point where it explodes into outright confrontation, (something of the sort can be seen in countries around the world today), and when this happens the fight then becomes all-or-nothing. That is 1 side becomes the outright winner and the other the loser. If the ruler loses then either the ruler gets executed, as was the case in Romania in the latter half of the last century, or perhaps the ruler is given the chance to flee into exile.

The point is, that by the time conflict erupts within a country the opportunities for a peaceful and negotiated transfer of all or part of the rulers power is generally lost and so monarchies tend not to evolve into parliamentary or democratic monarchies. Of course, this is a generalisation and over simplified, but for the purpose of your question I hope it provides something of a an answer.

PS, as a British national I cannot agree with your statement that Monarchs are symbols of national unity and pride. Even a cursory examination of the history of the 'british' royal family (many of whom throughout history could not even speak english) shows them to have been ruthless in their determination to retain power, and careless towards the sufferings and plaints of the people they governed.

The examples you gave were either deposed through a revolution, or lost power because the former monarch chose the wrong side and was seen as complicit in leading the nation to ruin. If the populace was upset enough to end royal rule, why would they tolerate a reminder of their unhappy past living lavishly in their midst?

The British monarchy, which you mentioned, is a case where the king gradually lost power through ceding it to Parliament. There was a somewhat amicable transfer of power without lasting bitter feelings among the public and political classes. This facilitated the idea of a 'constitutional monarchy' in which the nation has a sanctioned figurehead who also serves as a reminder of their glorious past, while the actual decisions are made by a democratic caucus.

Some of the reasons to exile ex-rulers (kings, dictators, even PMs out of political favor) are:

• Prevents them from rebuilding a network of loyalists for a possible counter coup.
• Prevents discussion on the legitimacy of the incumbents especially when the transfer of power was disputed.
• Removes an unnecessary drain on the state exchequer.
• Security considerations, especially if the ruler was greatly disliked in public.
• They may simply exile themselves out of shame at losing their position or to avoid conflict.

This is because the forces that overthrew them used to consider the monarchy as an alternative source of power that commanded loyalty of thousands of people. In case of any crisis, the monarch could have the power to overthrow the democratic forces, especially since many in the administration and army (not all of whom can be removed) are expected to remain loyal to the monarch even after constitutional monarchy is declared. Something similar to this was observed in Nepal. In England the parliament gained power only gradually, and so the monarch was generally not a direct threat to the power of the elected representatives.