This is true for so many reasons. I will list a few below. But, the sad thing is that a lot of pilots who carry people in their jump airplane do not have much experience and they have the minimum qualifications allowing them to fly the aircraft. Here are a few reasons why small aircraft have more accidents.
1. Lots of aircraft are old and poorly maintained.
2. Aircraft performance manuals are written to show best case performance when aircraft are new. But as engines get old, they do not perform as well and can't carry the loads advertised.
3. Accurate weight and balance during preflight doesn't always come out right after the aircraft is loaded. A young pilot might think it is no big deal.
4. Weather can throw everything off with high winds while pilots are in the clouds. Lots of pilots are capable of flying in clouds on instruments, but don't take into account that the wind is blowing them closer to a mountain. If they are not flying on an airway, or have accurate GPS information, they can get blown into a mountain. This has happened several times in Hawaii in the last 10 years and is the cause of lots of helicopter accidents.
5. There are lots of cases where pilots ran out of gas because they flew a route many times before and thought there would be no problem to do it again. But the aircraft wasn't quite full, or there were stronger head winds, or a fuel leak and the pilot didn't notice low fuel until to late.
Bottom line, the more training and experience a pilot has really pays off. Also, newer aircraft do not have as many maintenance problems. One study I read reported that the pilots with the highest risk have between 500-1000 hours because they have enough hours to be confident, but not enough hours to have seen a lot of real problems or emergencies.