Question

the metre is defined as the distance travelled by light in 1/299792458 of a second. why didnt people choose some easier number such as 1 / 3000000000 of a second?

Answer 1

We needed a standard to measure distance, we chose a specific length and named it as metre.
The metre was originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole. It involved measurement of a big distance, distance by hand and tough calculations(triangulation).
The problem with this approach is that the shape of the Earth is not an exact sphere, therefore there was some error in the distance measured so there was an error in the metre definition itself.
In 1889, it was redefined in terms of a prototype bar composed of an alloy of 90platinum and 10 iridium. The metre was defined as a distance between two scratches on the bar at 0degree Celsius. Temperature was mentioned because length increases with temperature.
In 1960, the metre was redefined in terms of a certain number of wavelengths of a certain emission line of Krypton86.

In 1983, the current definition was adopted,as the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom at rest.
You see it was not metre that was defined from the velocity of light, it was the other way around.
The fact that this constant is so very close to 300,000,000 - is a pure coincidence.