Why does Litecoin have lower transaction fee than Bitcoin? Is it only because LTC doesn't have as many users as BTC? Or do the faster confirmation times also help with lowering fees? 

Thanks
Litecoin's blockspace supply is greater:


Litecoin's block interval is a fourth of Bitcoin's at 2.5 minutes
SegWit is activated, limiting blocks to 4MB weight instead of 1MB size. With leisurely adoption of the new segwit transaction format this would eventually allow a capacity equivalent of blocks with ~1.7-2.3 MB size.


Litecoin's blockspace demand is much lower: 


Bitcoin does about 250k transactions per day with the mempool never completely flushing out, Litecoin has just slightly over 19k, while it could do about 2,000k.


Bitcoin is operating with demand exhausting the supply continuously, thus finding actually a price for blockspace. In the past months we've seen feerates move between 1 and 540 satoshi/byte. Now that the latest hype has cooled down slightly, we can observe a daily and weekly cycle, under the week going from ~8 to ~400 satoshi/byte, dropping down to as low as 2 satoshi/byte on weekends.

On the other hand, Litecoin is operating with demand at approximately 1% of the supply. Miners appear to be observing a hard coded minimum fee of 
100 litoshi/B.