Why is it weird? Yes Chiltern led on the section between Bicester and Oxford but there was sufficient foresight in that the works for East West Rail, double tracking and sensibly including certain provisions for future electrification were included. It was delivered on time and on budget, showing the advantages of what can done when you don’t have to work around the constraints of a live railway.
The decision to do that work was taken nearly a decade ago. It’s been open 5 years. It would have been an extraordinary waste of taxpayers money to electrify a route that would not see electric trains for almost a decade, particularly when the decision to proceed with the next part of the route hadn’t been made. (Indeed it still hasn’t!). It would all have needed maintaining (at cost), some of it would have needed replacing, and most of it save structures themselves would have had around 20% or more of their asset life doing nothing.
For some intermodals (i.e. going further north) I can see it being more popular than Wolvercote - Leamington (- Coventry - Nuneaton) as it is effectively grade separated at the WCML connections. Southbound advantage slightly more useful than Northbound.
And the best route for So'ton - Daventry as no inner GWML or WCML running.
Capacity Bletchley - Daventry might be an issue at certain times of day. @The Planner would know better than I do.