Why isn't "Enterprise" spelt "Enterprize" in US English? [closed]
For one, because the etymology is different.
-ise (-ize) is a causative suffix in formalise, realise etc. (to make something formal, to make something real...)
But enterprise is not "to make something enterpre" or similar (whatever that might mean). The prise bit comes as a past participle of French prendre (to grasp, to take).
Another answer is that enterprize is actually attested, and was apparently used more than enterprise in the second half of 18th century (N-gram viewer).