[Yorkie]

My lavenders look a bit like that, because I haven't pruned them as well as I could (I didn't prune them at all some years  )

You've got a lot of old wood in the middle, as others have said. That is perfectly usual behaviour if the pruning hasn't been quite right. There's no point in pruning back now into the bare old wood, as the plant won't regrow from that old wood.

The others' suggestions are worth a try