Since Spark is a project at Apache, though, if someone wants to contribute a Redshift integration module to Spark, no one cannot stop them.
Projects at the ASF are governed by a Project Management Committee drawn from the wider community -- not a single company, not a steering committee where seats are bought.
The ASF is a 501(c)(3) charity, which means that monetary contributions are tax-deductible and therefore very limited in what they can be used for. The ASF cannot unduly privilege any particular commercial entity.
Credit to companies, like Databricks, who choose to participate in ASF projects under these constraints.