+1 for Saskhunter. One other factor is the impulse energy experienced by a scope. "IF" everything else were held constant, wider field of view (with the same eye relief distance) means bigger heavier optic components, having to be designed to handle the impulse: It is much easier to mechanically contain / constrain a smaller optic than a large one. But then again, it's only money, weight and / or more sophisticated mountings.
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.50 BMG: 1 Shot 1 THRILL!