Good question!
Our answer starts with our philosophy: we bring extremely high-value products to you though good engineering, simple construction, and complete standardization. We don't offer color options, tube options, tweak options, etc--because we'd have to charge about 1.5-2x the cost to consult with everyone about what the best configuration is.
For complete standardization, we need (a) new production tubes, (b) reliable, consistent supply, and (c) reasonable cost. The two tubes that meet this criteria for a product at Lyr's price point are the EH 6922 and the JJ E88CC. We ended up choosing the JJ E88CCs because, in our testing and listening, they were more consistent than the EH tubes, and they sounded very good for their price point, when matched with a modern curve tracer.
Are there better tubes out there? Sure. Are the JJs garbage? Not at all.
Raise the price to, say, $949, and lots of other options open up. But think most people would like a $449 Lyr rather than a $949 Lyr.
Speaking of which, perhaps a better question may be why JJs are used in amps that cost 6-8x as much as ours.