Why are seasonal immigrant worker programs so unpopular?

Immigration policy is difficult to optimize, first because some economic rents are at stake, second because people do not want to share the luck of being born in the right place and at the right moment with foreigners who do not have that luck. But even within that context, a policy of seasonal immigration should be easy to adopt, as everybody wins: immigrants are let in only when labor demand is very high and cannot be met by locals, and the immigrants leave when the labor demand is back to normal. And the immigrants are willing to go for it, as it provides good income that is valued as they return home. This is a winning proposition for everyone, yet such policies are rare, and when they exist, they are little used. Why?

Danielle Hay and Stephen Howes take the example of Australia, where such a policy has been adopted for the horticulture industry but little used. It appears growers are reluctant to hire seasonals even when they have trouble finding workers. Either they are unaware, or they are afraid of red tape, or they prefer to hire back-packers (illegals) who show up on their doorstep. So it appears that once more, the fact that illegals can be exploited runs counter to good policy. Again, I appeal that we should give give each worker, legal or not, the same rights. Another win-win proposition.