I have had an ongoing problem that I am guessing I am not alone in. This is a perfect example. The hints for 'ficou' are 'became' , "stayed" and "have stayed" but 'the city stayed poor' is not accepted. I've reported it countless times with increasing frustration: "We need you to be consistent." I yell. "If the hints are there, accept the translation that includes them. Or remove the hint that is not acceptable. It has happened again, and again, and again. I am tired of ranting to the faceless Owl, so I'm letting you guys have it. Maybe we should go on strike.. :.=}
Actually, I'm glad that we don't have to just copy the hints down word for word. The hints give valid translations of the word. However obviously not every valid translation will apply in every sentence. I like having those different meanings of the word given to me and then looking at which meaning applies in that particular sentence. I'm not a native speaker, but I have been reading Portuguese now for 2 years. I have found that the word ficar has dozens of meanings. For examples: got, as in ficou contento, furioso, cansado...; became, as in ficou evidente; stayed or lodged, as in ficou nos melhores hoteis; kept, as in ficou com muito odio; is located, as in Onde fica o hotel?; remained, as in ficou preso por oito anos; was, as in Pedro ficou muito arrependido; grew, as in ficou rico; stay, as in ficar alerta; to be, as in sua reputação pode ficar manchada por anos.
You are right: "ficar" means "to stay". However, it can also mean "become". When I read the sentence, I instinctively thought the city was wealthy before something really bad happened. I don't know if it will help, but let me give you an example: Estive contente, até ouvir as más notícias. A partir daí, fiquei triste (I was happy until I heard the bad news. After that, I became sad).
I see "ficar" in a place or with someone means "to remain." With adjectives referring to the subject it seems to mean "become," to change state in some way. Can a native speaker clarify if "ficar" sometimes also means "stay" or "remain" when linking an adjective to a noun as in this sentence?
Subtitle from the site "businessinsider.com" describing the plight of Bridgeport CT:
How Bridgeport Got Poor In The First Place
Como Bridgeport ficou tão pobre inicialmente.
Because this is a subtitle, short words were used to save space. Better English would be:
How Bridgeport has become so poor
Como Bridgeport ficou tão pobre.