I never left the real world. And give a lot of credit to "what if" thinking.
The regulations provide guidelines to the minimum required for safety at the time of the installation. They pay little if any attention to making the installation easy to maintain or repair in the future.
Laying cables on the kitchen floor is not "illegal" under the regulations but it is a lazy and thoughtless way to carry out an installation. Are you saying that nothing can ever get to the floor where the cables are laying ? It is unlikely that a bottle of bleach in the cupboard will leak but such things do happen.
If the void behind the plinth is sealed water tight then lack of ventilation could result in mould growth and that can damage cables.
Supporting and protecting the cable at time of installation is a bit of extra work and expense, to replace the cable after damage would be inconvenient and time consuming and in the worse case could mean removal of parts of built in kitchen units.
