Gulf war 1 was 25 years ago, and that marked the last US conflict without ubiquitous precision guided weapons. That's probably right around the time the A-10 went obsolete.
In Syria... well, we could have used just about anything, from the AC-130 to the gun on the F-16. Fuel trucks are a pretty soft target.
Gulf war 1: Destroyed more than 900 Iraqi tanks, 2,000 other military vehicles and 1,200 artillery pieces for the loss of four A-10s
Syria 2015: Single A-10 takes out 116 ISIS fuel trucks https://www.youtube.com/watch?v=dQ37y0yeSgc&feature=youtu.be...
It still has it's uses. Also consider the costs - if you're using a high flying F-35 and laser guided bombs they'll cost I don't know $20k each and it can only carry a few so the cost of taking out fuel trucks would quite likely be more than the value of the trucks. A big old cannon can probably do it quicker and much cheaper.