Except that they're the ones that basically opened and controlled these trade routes, sent explorers out left and right to find better ones, funded expeditions solely focused on how to improve and expand trade, fought wars over trade and so on.
The Europeans *did* drive trade and, in fact, coffee, sugar, textiles, and so forth were driven from a trading standpoint by Europe in terms of money, volume, effort, national goals, you name it.
During the colonial era, the europeans colonized, subjugated and dominated much of planet Earth over trade. Their merchants profited mightily and very much more so than the locals they did business with in places like north africa, the middle east and asia. That was actually the point - buy low and sell high. The trade lines and the way they pull tends to reflect this.
I can certainly understand wanting to have Tunis or Morocco (Safi) be a dominant trade power ahead of Sevilla - but then what you're really saying is that they should be able to achieve economic parity in trade wealth when, in fact, either country being able to best Spain in trade income would be a good bit more "silly" it seems like.
*However*, rather than be unhappy with the trade lines, play the game to dominate them. So, yes, Tunis isn't a great place to try to build up trade power and make money; however, if you go conquer Alexandria, it turns out that with the addition of Aleppo you can basically dominate trade in terms of the money you make by driving Indian and Central Asian trade into Alexandria.
This is a big buff to Alexandria in 1.8 btw. In 1.7 and before, Persia went straight into Constantinople and thus making Alexandria into a huge money maker was perhaps possible, but extremely difficult as compared to simply getting Constantinople (simply - lol ). But with 1.8, if you're anywhere around, from Morocco to India, drive for Alexandria, pick up trade ideas and lay your merchants out to drive trade there and you'll soon enough have Alexandria as the new Constantinople. Given it's location and the relative weakness of the Mamluks being between various rocks and hard places (check out Ethiopia's starting tax base - they've gone from protectorate food to potential beast), driving to Alexandria and making it into a dominant trade hub wherein you drive all your trade power vis-a-vis your conquests, seems a very valid approach to countering European and Ottoman trade power.
Just a thought.