Why Matisse Painted With A Really, Really Long Brush?

Some think it was because he was too old and sick and bound to the chair and bed. There are however paintings that show him standing and painting with a long brush, so there must be more to it. Velazquez also used a long brush, so what was it that caused these artists to pick up the long brush?
Unfortunately its too late to ask them but luckily today there is artist Bob Booth, who uses a 1.2 metre long brush. Bob says, “The advantages of using a long brush are huge!”.