It is not an ending a casino wants and they don't want to lose money for cheaters and see their reputation damaged by cheaters. They don't want to waste resource to handle such cases and invalid scam accusations from cheaters.
I think rules are reasonable and fair enough.
I looked at it and I think it won't get exploited besides the free spin is a chance since we need to spin it and there are null places on the wheel wherein we will not be rewarded with spins. In short, we need to gamble to get that free spin. And still, to get the reward from free spins, it needs some wagering requirement which in most cases, the winnings in free spins is depleted even before reaching half of the wagering requirement.