Without additional context (which perhaps you have and used subconsciously) that's not evidence that there's less demand - just evidence that the ratio of demand to stock is lowest. It could be that it has 2x the demand but they prioritised it and produced 3x as much stock, or it could be that a specific component makes one product easier/less delayed than the other to make (in which case equal demand could still lead to only one being regularly in stock).

If for example 100 people a year want to buy a product $A, and 10 a year want to buy product $B, and the company manufactures 200 $A's a year but only 5 $B's, then $B will be out of stock more despite being far less popular.

Or course this partly relates to how well a company predicts future demand when deciding how much of each product to create. But in many cases (though I would guess not when it comes to The Raspberry Pi Foundation) marketing therefore also becomes a factor - in that companies may see value in either creating slightly less than they expect there to be demand for, or artificially limiting / lying about stock levels, in order to get people thinking "wow it's out of stock so it must be popular!"