Yes, it does seem somewhat odd in our 21st century lives but without war he can't make any more money as there will be no prizes to capture.

But I think the larger overriding factor was death. Disease was much more likely to be fatal too (Fanny Harville for example, the worry over what we would consider minor today -I can think of at least three other Austin novels where sore throats and colds could potentially lead to death) without antibiotics and modern bone setting. I thought the first time I read the novels that the concern in these situations was overblown until my mother pointed out her grandfather in 1920 died of an infected toenail.

Wentworth could die easily on a normal voyage, as poor Dick Musgrove did; with war at least he'd die rich.