Because it is an escalation that does not need to occur. With more and more offenses becoming felonies, the “raise the bar” mentality of legislators will come to a breaking point, where everything is a felony. These folks would be better served with a sentence of community service but now are facing 2-3 years.
“Grand theft” vs. “petty theft” is based on the value of the goods stolen. This is not new. A quick search shows that the carts at Walmart are valued around $2,500. If they’d stolen a car valued at $2,500, it would be grand theft. If they’d stolen electronics valued at $2,500, it would be grand theft. Why should this item be different?