British people have been applying in droves, but turned away for many reasons.
Also the wages are often minimum wage or close to, with deductions removed for accommodation etc...
Hard for a British person to afford to do that and keep up rent/mortgage on their proper home.
Then throw in the fact that most unemployed people are in towns and cities with no access to private vehicles to be able to travel to these farms.
Far from a case of feckless lazy Brits.
The likes of the French pay proper wages for their fruit pickers, including all benefits and rights, and as a result get French people picking the fruit.
Here it just isn't possible for most British people for economic reasons.