Gobowen is a railhead for Oswestry, which is a bit larger. The new service only makes sense to be as an easy extension of an existing service. As pointed out by
@LNW-GW Joint, the map on the DfT's website shows it to be an extension of the daily Wrexham service, the stock for which comes from the depot in the morning, and goes straight to the depot again in the evening. Extending it to Gobowen doesn't directly impact any other diagrams, it just needs it to spend less time at the depot. Low hanging fruit, and all that...