A Type A transport (seen here with a Kalahati Tuul)
A DDS Upgrades spokesman working on the Type A contract said the older ships had been considered for refurbishment too but are simply too old to make it worthwhile. "To get any more than 10 years more out of them we'd have to practically rebuild them, its therefore much more practical for the Clones to replace them with new ships which would last for at least twice as long and have improved performance."
Another reason for replacing these aging ships is so they can be sold to other navies as they recently did with Artic who bought 3 ships. The HCS can sell them cheap to customers after a minor refurb to keep them going for 5-6 years more and this is considered a way into the lucrative spaceship export market the DDS have had largely to themselves so far.