Seized EGR valve

Had the Egr valve replace after it had seized by Birchwood of Eastbourne. Although they were very busy they took the time to fit me in as we were going on holiday next day, cost £239.12. My thanks to them for doing it in time. Now what causes the valve to go as oil had sprayed out onto the engine via the relief hole. We have only done 45967 miles and its had regular services as required, also lucky for us we we only came back from holiday week before where we had done 1350 miles towing caravan.