Actually Germany could easily have provided more resources to its Afrika Corps had it not commit itself to Barbarossa. The most important clue is on Rommel's continued badgering to the High command for more supplies. It means infrastructures were not the issue, the problem were the matrials.
Well, Germany generals had a tradition of ignoring logistic issues. This problem had repeatedly happened in East front: they rejected the logistic department warning of difficulties in overstretched supply lines and limit in infrastructures again and again.
The same mistake was made by Rommel as well:
1. he convinced Hitler that he could defeat British in Egypt without occupying Malta, which proved to be a huge mistake: Malta became the key base disturbing his supplies later;
2. Just like you, he also believed these logistic issues could be overcome: for example, he kept asking for more trucks to supply his army (already 20% of all Germany trucks) but refuse to listen that DAK had no more spares.
Infrastructures were issues before you fix them. However, fixing these issues means you have to ship building material, harbor equipment, construction workers first instead of guns, tanks, fuels and soldiers. And it took a lot of times.
Again, Rommel refused to wait.
And we haven't started to talk about that over 600 miles supply route through desert yet.
Besides, had Hitler not launched Batbarossa, and with full focus on the North African to Egypt campaign, the Germans could easily committed men and materials to enlarging important docks in both Italy and the landing areas in North Africa to accomodate more ships.
Again, you ignore the logistics:
1. Italy didn't have a big enough qualified merchant ships to support a massive Germany force. She only got 786 ships size bigger than 500 tones. Within 2 years, the figure down to 324;
2. Italy navy was not strong enough to protect the shipping. She was inferior to RN in quantity and quality;
3. According to DAK, the material requirement for Rommel's division was 10 times high than the same division fighting in Russia, I don't know how Hitler is going to say about that.
Most importantly, don't forget RUSSIA. You simply couldn't turn your eyes away when a 5 millions solider standing outside your door. Yes, they were terrible in Finland, but you know they were getting better.