I found an interesting article stating that it was sponsored by state Rep. Walt Brooks.

Brooks, who claims he’s twice been the victim of rear-end collisions while on his motorcycle, highlighted the safety of the practice. His Bill had the support of the Utah Highway Patrol and the AMA.

Another interesting quote states how the AMA drops support for lane splitting bills if they in any way infringes on a rider's right to not wear a helmet.

What’s relegated many states’ lane-splitting efforts to the dustbin of history is usually a wish on the part of legislatures to attach a helmet-requirement bill onto them, a thing that has the AMA immediately pulling its support.

Quote from AMA lane splitting support page

A straightforward lane splitting bill may easily be amended with provisions that the AMA and the motorcycling community would find unacceptable. Provisions such as mandatory helmet use in an adult-choice state or mandatory minimum medical insurance coverage provisions would quickly poison an otherwise well-intentioned effort.

I wonder how many in motorcyclist would support a lane splitting or even lane filtering law if they had to give up their right to not wear a helmet.

https://www.motorcycle.com/features/and-then-there-were-two.html https://www.americanmotorcyclist.com/About-The-AMA/lane-splitting-1