I think the attraction to the Inland carbines over a GI carbine is twofold. First, the name is one people like because of it's history.
More importantly, some people don't want to mess with trying to figure out which GI carbine functions as it did during WWII. It's a gamble they choose not to take. While part replacement is as simple as simple can be with the GI carbines (albeit sometimes expensive) they choose not to have to spend time figuring these things out when all they want is a reliable shooter. Add the Inland name and it draws attention to Inland Mfg over Auto-Ordnance and others.
These folks rely on Inland Mfg to make a carbine that functions. Get past the break-in period and most will function fine. The question is, for how long. Shoot a few hundred rounds now and then and on calendar time they'll be acceptable for awhile. Well past the warranty period.