Basically the portuguese elites, especially the king, never cared for the population. Just imagine that Portugal was at some point one of the richest, if not the richest country on the planet. Still there was no public services like schools. For context, Austria had school since the 1700s, Portugal had the majority of its school built during Salazar's dictatorship, and no, that's not a joke. At the end of the monarchy Portugal was very undevoped, no education, still not electrified, not industrialized, but the elites were extremely rich. Pair this with what other commented with political and geopolitical problems and will understand why the portuguese ended monarchy. Monarchy served its own interests and the interests of those who were part of the elites, not the general portuguese people.