Goalkeepers tend to improve/mature a bit later in their career, so may be Stevens just isn’t quite there at the moment. It’s also difficult to find decent keepers who are prepared to sit on the bench week in, week out, especially if they’re at the peak of their career, hence why Stevens is good cover if needed short term.
Goalkeepers need to give a calming/reassuring feeling to the defenders which Eastwood provides in abundance, again down to experience/time.
I’m sure Stevens’ time will come e.g. tonight etc, but I think a more experienced keeper is needed over the longer term e.g. 4-8 weeks if required.