[Cupid]

I'm sure other processors have been considered.

They not only need to have an interface that allows the automated integration to do the required job, each implementation increases the complexity of the solution and therefore the support costs and therefore the risks of a failure of some kind increase.

In addition extra payment processors increase the accounting costs at the other end.

So the decision as to whether to implement any other processor has to depend on a high degree of certainty that it will be used by a significant number of users. Sadly it's been found in the past that some extensions that take a significant amount of work to implement, and have been consistently requested here, end up not being used very frequently.