Inference issue when an implicit method is promoted to an implicit function

[kubukoz]

import language.higherKinds

object Main {
  trait Eq[A]  
  
  case class Cofree[S[_], A](head: A, tail: Cofree[S, A]) //simplified
  

  implicit val intEq: Eq[Int] = null
  implicit def forList[A : Eq]: Eq[List[A]] = ???
  
  
  implicit def eqCofree[S[_], A : Eq](implicit
    S: implicit Eq[A] => Eq[S[A]]): Eq[Cofree[S, A]] = ???
  
  
  val a = eqCofree[List, Int]
}

This fails with:

-- Error: /tmp/scastie6251223766744740367/src/main/scala/main.scala:16:29 ------
16 |  val a = eqCofree[List, Int]
   |                             ^
   |no implicit argument of type implicit Main.Eq[Int] => Main.Eq[List[Int]] was found for parameter S of method eqCofree in object Main.
   |I found:
   |
   |    {
   |      def $anonfun(implicit evidence$4: Main.Eq[Int]): Main.Eq[List[Int]] = 
   |        {
   |          def $anonfun(evidence$1: Main.Eq[Any]): Main.Eq[List[Any]] = 
   |            Main.forList[Any](evidence$1)
   |          closure($anonfun)
   |        }
   |      closure($anonfun)
   |    }
   |
   |But method forList in object Main does not match type implicit Main.Eq[Int] => Main.Eq[List[Int]]

but if you use eqCofree(intEq, forList), it compiles.