It's the international standard for labelling components, it overcomes the problems of decimal points being missed - you use the letter to replace the decimal point, a 'k' is far easier to spot than a '.'.
reasons for using units (or multipliers) instead of decimal point (or decimal comma) is that it is not only shorter but also more reliable. markings on some parts easily wipe of just by touching them with fingers.
dots are quite small and easily lost...