Your arguments are based on logical impossibilities and legal improbabilities.
1. They do enforce their laws. They do patrol areas that are frequented by undocumented refugees entering France. I'm sure that when they detect dingies leaving without completing the formalities. they may prosecute, but that would merely encourage those refugees to apply for asylum in France. Clearly those refugees are intent on reaching UK, so they'll probably try again, and again.
I know they do prosecute people smugglers when they catch them. If France wanted to prosecute the refugees for infringing French laws, how would that be possible, once the refugees have applied for asylum in UK? Certainly UK could not prosecute them for infringing French laws.
2. I'm sure that you are aware of many laws that are fine as drafted, but in practice are difficult to enforce, and may prove inordinately expensive and provoke adverse publicity again if enforced. Then there is the normal test of the DPP:
3. To register an exit, by boat, from a country, one is required to leave via a port of exit, to have one's passport stamped, etc. This is clearly impossible and counter-intuitive when refugees are leaving from a beach in Northern France. There may be not be any passports to be stamped. Again, how would the French hope to enforce, such processes, or to prosecute refugees that have not complied? The boat was not registered, how would the French identify the occupants?
4.
5. The logging of a Passage Plan assumes one has a plan, however sketchy.
When seeing what is required in a Passage Plan, it is obvious that it would all be unknown for the refugees, or so vague as to be nonsense.
Of course logging a Passage Plan would be counterproductive if secretly leaving from a beach in Northern France.
How to prepare a passage plan
www.jollyparrot.co.uk
You can see that your arguments are impractical.