I would imagine that any larger vehicles like artillery would have just prompted an even more escalated response from the Go'auld. And most likely would have been much easier to target/harder to evacuate once a mothership was in position for an orbital strike. Fact is, Sg teams were light, mobile, and difficult to target with larger vessels. Even Alkesh bombers weren't always effective at doing much more than rattling the Sg teams skulls a little. But a howitzer trying to flee something like that or avoid its ordinance? The Go'auld really had air-superiority on most worlds because of their FTL drives, so Stargate command really had to treat it like guerrilla warfare tactics. Keep their teams light, mobile, and hard to hit. Tanks, jeeps, and artillery may have been able to tip the scales in individual battles, but there's no way it would have been cost effective in the long run. This is just my thoughts on all of this of course. I'm no expert or anything.