I do think why Beye is sold is because France has a strong tradition of blooding youngsters. Those who aged 28 or above are likely to be sold or offered a short term contract,
and only those established internationals like Barthez will be managed to get a retirement like contract.
This also applies to Holland. Lots of youngsters getting chance to play, and they will sell them for a large sum of money. That's how the club runs, and players like Beye will prevent them from providing space for youngsters. Thus it is a lot easier to buy established players in France like Beye rather than rising stars like Gomis.