The Corran Narrows is where Lower Loch Linnhe gives way to the upper loch. The ferry across the narrows is still of course very much running (at least when it is not broken-down), providing a much quicker, yet very expensive (alas no longer free for foot passengers and cyclists) land route to Morvern rather than driving all the way round Loch Eil. It also provides a long route from Oban to Mull via the Loch Aline to Fishnish Ferry, but this does avoid congestion on the Oban to Craignure ferry if you haven't booked (and the all too frequent cancellations at the moment).
Because there are not that many interesting anchorages in the loch, I suspect the few boats you do see here are either local or on their way to or from the Caledonian Canal. Indeed, in mid April I have sailed up and down the loch and seen not one other sail. But it is a grand place with remote mountains to the west and not quite so remote but higher mountains to the east (along with some main road traffic noise and the suburbs of the not-at-all-pretty Fort William). And 'The Ben' looms at the head of the loch (Ben Nevis to the non-mountaineers). So nothing much has changed in the last 120 years since Frank Cowper wrote: "I don't think yachtsmen generally, if cruising in a sailing yacht, will care to go up these lochs, unless for some special reason" (Sailing Tours: The Yachtsman's Guide to the Cruising Waters of the English and Adjacent Coasts, Part V, The West Coasts of Scotland, the Orkneys, and the west coast of the North Sea. Frank Cowper, Upcott Gill, London, 1896).