There's explicitly a test to make sure that Open Access services are 'not primarily abstractive'.
Yes, the key word is 'primarily'. Even if not primarily abstractive, it doesn't stop Hull Trains and Grand Central being at least in part abstractive which they clearly are with regard to shared flows, both through LNER offering reduced fares at the common stations and the need to share revenue.
Ultimately the taxpayer is funding competition and what could be considered unnecessary duplication on the routes.