I think the Thunderbird is a great bike for the people in India where a big 500cc thumper cruiser is in demand. It's kind of a low cost answer to the peoples desires to own a Harley.
The new UCE Thunderbird isn't the first Thunderbird to be sold in India. Royal Enfield also offered it with the old engine design.
Why isn't it being imported into the US?
I can't speak for Kevin who decides these things but IMO there are a lot of Japanese cruisers here with more power and features at lower costs so who would buy a machine made in India?
The B5, C5, G5 and Cafe on the other hand are truly unique in the US.
They offer antique styling and handling with modern reliability. They have no direct competition from other makers and for the people who like true retro styling their prices aren't too bad.
As for the Cafe model, it has a bunch of things that make it attractive to me.
More power, a unique double downtube frame, rear disk brake, classic styling...
On the other hand, I gave up knee dragging years ago and the rear set foot pegs and clip on handlebars and the crouched riding position that goes along with them doesn't suit my antique body anymore.
If I bought one I would want to change the bars and rearsets to match the other RE models but I don't think the frame is set up to allow that without welding on some extra mounts. The hydraulic rear disk brake master cylinder would also require moving so there would need to be quite a bit of revising to get it like I would like it.