Aircraft flying as high as secure?

Currently, large aircraft often have to fly at altitudes above 10,000m. Why fly so high? Low flying is not safer or what?

Why should civilian airplanes keep 10 km altitude when flying?

This is the exact opposite, the higher the flight, the more secure it is. Around the earth there is a very thick atmosphere , within the lowest range of 10,000m called the troposphere . Thunderstorms , the rise and fall of air currents all work in this area, so it is very exciting. If flying within less than 10,000 meters, the aircraft will not be able to avoid the influence of downward air flow so it cannot fly in a stable manner; sometimes it can be struck by lightning, but if you encounter water particles and ice particles with low temperature, the outer shell may be frozen.

Therefore, if not in a forced situation, the aircraft should not fly too low, but if at altitudes above 10,000m, it is relatively quiet at this altitude, the aircraft can fly in a stable way, At the same time the air above it is very thin, very little water vapor so the outer shell is not afraid to freeze.