The reason for this is that Regulus A has a very close companion, Regulus AB, which is thought to be a white dwarf. The white dwarf is the remnant of a more massive star that evolved faster than Regulus A and transferred some of its mass to it before becoming a white dwarf. This mass transfer increased the hydrogen supply of Regulus A and extended its lifespan. However, it also increased its rotational velocity to a very high value of 347 km/s, which makes the star oblate and causes it to lose mass through a stellar wind.
Regulus A is expected to leave the main sequence soon and become a red giant, which may engulf its white dwarf companion and trigger a nova or a type of Ia supernova.