Sellers decide things like this on a risk  vs reward basis.

In the case of using a courier like Aramex, the risk is the dissatisfaction rate from their customers when a problem is experienced, and the reward would (I'm assuming) be cheaper shipping rates.

If the risk outweighs a reward, it is generally incentive enough for a seller to adjust the practice and change carriers.

If a seller does not change carriers, it can be logically presumed that the reward outweighs the risk, which in turn suggests not enough customers experience problems, and / or that the problems experienced are not great enough to cause complaint. 

(I don't like Fastway / Aramex either, if but just because I've found them to be the slowest couriers in Aus, and because if I miss a delivery, the drop-off point is strangely quite far from where I am, but you have to apply rational logic to the situation in its entirety - a seller isn't going to change their entire shipping model just because I say "I don't like it", IYKWIM).