Quoted from RCIV:
In interview with Brian Eddy on Dead Flip the concern was the durability and reliability, but would be cool if Grogu would evolve to be animated one day.
I think the concern is legitimate, and they probably made the right call here.
Plopping a $50 Hasbro toy on the playfield and "circuit bending" it to interface with a node board is easy enough to do, but there is absolutely NO WAY such a toy would remotely last as long as the rest of the machine, and it would likely become an ongoing headache for Stern's service department.
Designing and implementing an appropriately robust mechanism with a proper metal chassis/actuators/gears, brass or ball bearings, decent stepper motors/controllers, etc. would almost certainly add way too much to the overall costs to even consider for the Pro model, and might even be a challenge for the Prem/LE as well (ie. other features like the elevating playfield would need to be sacrificed).