Maybe they just cared less about destroying infrastructure/killing civilians in Syria.
I suspect though that whilst Russia likes to portray that it has a modern military with high tech equipment, the reality is that their good stuff is in short supply and the vast majority of their forces are still using soviet era equipment.
Edit: So Ukraine are reporting that Russia's losses so far are:
- 14 aircraft (13 attackers (SU-25 and other CAS) and 1 IL-76)
- 8 helicopters
- 102 tanks
- 536 armored cars and APCs
- 15 artillery pieces
- 1 Buk air defense system
- 3500 soldiers (dead, captured, wounded)
I expect Ukraine are inflating the numbers for morale but honestly even half or a third of that in 48 hours is surely a massive blow. I wonder what Ukraines real losses are thus far, I saw on BBC that a military hospital in the east has all 400 beds filled with wounded, grim.