I have a situation where a SUV > 6,000 lb. GVW was purchased in September, 2021, and used for business.  They only drove 1,000 miles (90% business use), yet it seems that they can bonus depreciate/Sec 179 almost the entire purchase in 2021.  What happens in future years when (if) business usage drops below the current 90%?  It makes no sense to me that so much can be written off in 2021 with so little mileage driven, but I cannot find a single thing that contradicts this.

Any input/thoughts will be appreciated.  Thanks.

Mike