Historically, there was a period of time when there were no poor people left to take Zakat, everyone paid their share, and no usurious transactions permitted.
This is worth treating carefully. There are sources like Ibn Kathir and al-Tabari writing centuries later which claimed that Zakat collectors would return with unspent funds because eligible recipients could not be found. Even if we take this at face value, that's a leap from there being no poor people left. Did it apply to the entire empire or only a few regions? How likely was the collector to actually find recipients if they existed in a given region? etc...
Point is to refute the claim the current situation in some Muslim countries is caused by Islam, instead of it being a direct consequence of colonialism.