Young people now were likely to be put off by the cost of getting a motorcycle licence and were more likely to opt for just a car licence, Mr Purcell said.
Bigger, more powerful bikes were one factor among many that could cause crashes, he said.
"There are a lot of guys that once they are over 40 and they are free of children, they get back into riding and the bikes these days, they are a lot bigger.
"It could well be a factor that bikes are bigger and heavier, and generally the roads are busier and there's a lot more traffic on the roads and people are always in a hurry."
Fatal crashes occurred for a number of reasons, and overconfidence and speed could sometimes be a factor too, he said.
"If you put 10 factors in there you wouldn't be wrong - it's a complex issue.
"Really at the end of the day a motorbike rider has got to be responsible for their actions and has to ride to the conditions - but saying that you've got to be prepared for anything that comes round that corner... that's the nature of the game, if you come off a motorbike you are going to get banged up a lot more."
Mr Purcell said at a recent session held with ACC many bikers had been enthusiastic about undertaking further training and improving their skills.
He encouraged bikers to upskill when possible, invest in good gear and maintain their bikes well.
"Make yourself as visible as possible. I wear a high-vis yellow and black helmet, I wear a high-vis vest. I'm fully covered head to toe."