It's very strange what they don't discuss, especially when it seems to answer supposedly unanswerable questions.

I rooted around in wikipedia and Malawi has FAR more people than the land can support. They have a top down demand they must grow maize although the land and climate are very unsuited for maize. Why? Unsurprisingly they have had severe recent famines unlike Rwanda. If they had capacity they could survive a minor shortfall in rain but they have more people than the land can support so the famines are very rough. They have about 3x the agricultural land as Rwanda but its not suited to maize but its demanded they grow maize. Maize will only grow with massive fertilizer imports which they cannot afford and occasionally politically/economically manage to totally screw up, alongside Maize is traditionally dependent on very reliable rainfall or post industrial era advanced irrigation which they don't have.

I would estimate the geography of Rwanda will support about 20M people, luckily they have about 14M. They can coast thru some rough agricultural times and they've developed enough industry and trade that they can import their way thru short term minor local problems.

On the other hand Malawi can only support maybe 15M people reliably, unfortunately they have about 22M. When the rains don't come or the politicians screw up the fertilizer imports, they die.

Its very difficult for them to "advance" beyond subsistence ag without enough to feed everyone and ag policies seemingly intended to be self destructive.

I don't know why they "have to" grow maize despite it resulting in starvation. Historically this type of thing is caused by someone making a huge profit or attempting to maintain control. Regardless of cause, until they can eat, they will not advance.

After eating dinner tonight they can dig a mine or build a factory. Oh wait there is no dinner tonight. Well then. And so they remain very poor, permanently.

The country, as a plot of land, is quite wealthy. $22B is a lot of money. If they had, say, 3M people as a population they'd be in position to become the next Taiwan. Taiwan's GDP per capita was about there in the mid 80s before they really took off. But they have over 20M people probably 30M soon, so they'll live in poverty, permanently.

In Rwanda an unusually good harvest means a new mine can be opened and they will "permanently" be richer. In Malawi an unusually good harvest means the people who would have starved to death this year now won't starve to death until next year. There will be no permanent improvement of anything in Malawi.