They do have hot weather leathers for motorbike riders. A quick Google search brings up a heap of places that sell them, and the link below is from an ABC science show in 2016 about the subject.
Exploring the forefront of science and technology, Catalyst brings you compelling stories looking at the latest in science from health and medical breakthroughs to astronomy, environment, and agriculture.
www.abc.net.au
Even though full leathers (pants, jacket, boots and globes) are hot in summer, it can mean the difference between permanent scarring and skin transplants.
Helmets should be compulsory in any country.
There also needs to be better laws so other motorists have harsher penalties if they clean up a bike rider, as well as better driver training for all motorists. Over 90% of motorbike riders that get injured on their bikes, are hit by motorists that aren't focusing on what is happening. And because the impact is between a 1.5 tonne car with built in safety cells and lots of other safety features, vs a person on a bike, we all know who is gonna come off second best.
Motorbikes and associated clothing needs to be brighter coloured so the riders and bikes stand out better on the road. When you have people on black bikes, wearing black leathers, on a black road, it makes it harder to spot the rider. Having bright coloured leathers or even wearing a fluoro yellow or pink safety vest can go a long way to helping other motorists see the riders. But there's always going to be some ahole that doesn't look and pulls straight out into a bike going through an intersection.