Even though many farms are lacking in the trace minerals, they do add lime.
I think the main problem is that everything is picked before it's ripe. That would give you a low reading because things that ripen before they're picked are sweeter.
You are reading the Sugar not the minerals. Common sense tells us that if it was left to get sweet before picking it will also have had time to reach the proper level of alkaline minerals.
If you've ever been to FL and picked an orange from the tree, you will see it's so much better.