It's a Catch-22. T/C produces a sidelock but the sales are light. They say: "people don't want sidelocks." The public, on the other hand, may be saying: "we want a longrifle or a half-stock that IS something and doesn't try to be too much at once and so ends up being not much at all". Many of us are here for the history and not just because it loads from the front and goes bang.
There must be a market of muzzleoladers who would kill for accurate representations of historically significant muzzleloaders. A 1st Model Bess, a Charleville, a 1795 Contract Rifle (they missed the "200th L&C anniversary special addition" boat on that one), a plain Revolutionary era rifle, a Leman or a Derringer trade rifle, a Northwest Trade Gun (tell me you wouldn't like one of those in 24 bore made to T/C quality ~ they should be able to make a dandy for $500 or less), a Tennessee squirrel rifle to take the place of the sadly defunct Dixie version - but with a strong lock.
If they only did two: a smoothbore trade gun copied from a Wilson and a plain Southern Mt. rifle from a Bean with a straight but thin walled barrel. Not all shiney but a matte finish, even blued would be OK because those that wanted could take it down with Naval Jelly. Don't need the hooked breech, just pins and a screw. Don't need high & adjustable sights, just simple dovetails. Sell a small file as an accessory in a shrink wrap.
Ruger got brave and sold a revolver without adjustable sights and SASS sprung up overnight. Well, that may not be exactly what the root cause was, but look at what's happening there!
Maybe someday.