Automobile leases are typically fixed (closed end in your terms) by design because of the nature of automobiles - they depreciate. That is, they lose value predictably over time. A lease payment is based on the dealership doing math on how much depreciation they expect to occur in a given time frame, then applying a money factor (interest rate) to that amount of lost value, and dividing it into equal payments over the given time frame. In order to do this math, the dealer needs to know what the depreciation is, per unit of time.
But it's important to note that the depreciation for a car does not follow a straight line - that is, the depreciation in the first month is very different from the depreciation in the 30th month. Because of this, the dealer needs to fix the duration of the lease ahead of time, in order to draw a line in the sand in terms of fixing the depreciation they have to divide into monthly payments. With the fixed time frame, it doesn't matter if a given months' payment covers that specific months' depreciation, because the total depreciation is spread out over the total time frame.
If a dealer allowed for a lease to be open-ended (that is, terminated at any random time), they would have no way to calculate a monthly payment that would work out to the total depreciation over the (unknown) total life of the lease. If the payment was calculated based on 30 months of depreciation, but then you turned the vehicle in after 3 months, the three payments you made would not cover the 3 months of depreciation (because vehicle depreciate quickly at first). Conversely, if you calculated the lease for 30 months, but then turned it in after 40 months, you would have overpaid for those last 10 months.
Other types of assets that are leased (i.e. land) are typically not considered to depreciate. Or, the depreciation is handled via a different mechanism than the lease itself. Because of this, the lease payment can be essentially fixed on a month by month basis, without having to know the duration of the lease upfront.