How do I manage waitlist abandonment?

I'm running a high-end, limited edition product line where demand consistently outstrips our manufacturing capacity. Every time we launch a new collection, our waitlist becomes a nightmare. Potential customers sign up, get excited, but then mysteriously disappear before completing their purchase when inventory becomes available. I've noticed our conversion rates from waitlist to actual sale hover around a frustrating 35-40%, which means we're losing nearly 60% of potentially eager customers. It's not just about lost immediate revenue—it's about the marketing effort and customer acquisition cost we've already invested in these interested buyers. Our current process involves standard email notifications, but they feel impersonal and don't create any real urgency. I need a sophisticated strategy that not only notifies customers about product availability but also compels them to complete their purchase quickly and decisively.