There was no "Indian" motor to Polaris to stick with. The first iteration of 'Indian' from CA wasn't 'Indian' at all except for the name on the tank. The entire motorcycle was simply assembled parts you could have purchased from J&P Cycles and assembled in your garage
The second iteration of 'Indian' out of NC was another H-D clone Evo motor with rounded cylinders and a ton of chrome. Build quality was vastly improved but no one at that version of Indian had a clue about the market. They were mostly venture capitalists and everyone knew the brand was soon to die again.
When Polaris bought the rights to the Indian name, they started with, more or less, a blank sheet. But bear in mind they had many years of designing and building Victory Motorcycles to rely upon. Many of those same Polaris designers were simply used for the Polaris Indian line. The Polaris designers that had so many unique ideas and direction for Victory, apparently had nothing left for Polaris Indian. They simply copied many decades old design cues from actual Indian motorcycles. Then incorporated (copied) the work of other designers into their version of an Indian motorcycle. Again, Polaris didn't actually add much of their own touches to Indian and they still haven't. The first Polaris Indian motor had to be an air cooled twin, downdraft exhaust, lots of chrome etc etc etc. It had to had big fat valanced fenders etc etc etc. Again, these were all decades old design cues that Polaris incorporated. There was nothing 'new' to the bikes.
IMHO, the first series Polaris Indians were modern versions of decades old actual Indian designs. The second series mostly copied the aesthetics from H-D. The third series of Indian's most successful bikes, The Scout and the Challenger, came directly from the Polaris Victory Motorcycles team years before.
The Indian Scout was 100% designed and built as a Victory. It was shown to the Victory dealers as their long awaited entry level bike. Only to be taken back by Polaris and slightly redesigned and then released as the Indian Scout. In the redesign to make the Octane the Scout, Polaris mostly just changed the rear suspension angle (hurting, not helping it), changed the gearing in the transmission (less performance) and changed to aesthetics to say Indian. Nothing, absolutely nothing on the Scout said 'Indian' but the name on the tank. But it sure looked like it belonged in the Victory line up.
The Indian Challenger was also 100% designed and built by Polaris Victory to be the new version of the Vision/Cross Country. The engine and drivetrain along with design drawings were also shown to Victory dealers so they could see what to expect soon. Again, Polaris pulled the design from Victory, killed the Victory brand and then released the Challenger as a new Indian that again borrows heavily from H-D design aesthetics.
I honestly don't know what happened to the design teams in the motorcycle division at Polaris. They just don't seem to have anything unique left in the tank for Polaris Indian. Sure they incorporated better bluetooth and Ride By Wire. But aside from that, there really isn't anything new and exciting. As has been said, the Indian name seems to dictate they keep decades old design cues. Very similar to H-D. The older Indian owners seem to prefer the aesthetics of 'older' looking bikes to the aesthetics of the Challenger type.
Of course the Challenger is a powerhouse, it was designed for the muscle brand at Polaris, not the nostalgia brand.