Why do we still use seconds and meters as SI base units?

[Firestrider]

If

The second is currently defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.

And

The meter is defined as 1⁄299 792 458 of a light-second.

Then

Why can't we use a new system that a 'unit of time' = the duration of 1 period of radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom, and a 'unit of linear measurement' = the distance of 1 light-'unit of time'?

The only value that I know is true to nature is 0 in Kelvin/Rankine, corresponding to absolute zero.

 

[chroot]

Because people are more used to measuring fabric in units of "oh, about an arm's length," not untold powers of ten of wavelengths of radiation they cannot even see.

- Warren

 

[Gerenuk]

Only for the sample reason why some countries still use non-SI units at least in some areas. Because they believe that for applications it doesn't matter you say one number or the other. And so they stick to "their own units".
However in science it is quite popular to define units in such a way, that for example the speed of light and other fundamental constants are exactly one. Then you can drop them completely from equations.

I'm attaching my notes on this topic (it only lack the important h=c=1 case).