What is going on is called demand.
These rifles are selling fast and now are reaching a whole new group of hunters/shooters who have increased their popularity. It is not just older JM Marlin fans, but leverguns of all types are getting a lot of new converts.
Ruger has always dribbled out new guns. Ruger also runs guns on production schedules, so when a run is sold out there is a gap in availability. I have seen a lot of them at gun shows and they sell fast. At the LGS it depends on what the customer base of the shop is, as to what is actually in stock. Most will offer to order, but many people want to see and feel a gun before they part with cash.
The LGS will offer to order, but for myself, if it is a NEWLY introduced gun, especially a reintroduction of a classic, I want to see it in person first. I do not need to be the first person to have it, so why order it sight unseen. We all know gun magazines and gun press have "never seen a dud", so why take a chance.
I read about the Ruger/Marlin SBL and it looked interesting, but handling it sold me. I will get one, but not until I find a standard used stainless lever to replace the big lever, as I am NOT a fan of big levers. From the introduction of the original 1860 Henry and the 1866 Winchester up until "The Rifleman" TV show, folks managed to cross the frontier and take lots of game, and all while not wearing gloves

, gloves being the purported rationale behind the big lever trend.
I think Ruger/Marlins are out in circulation more than many of the assorted Ruger product announcements, which have always seemed to become available to see in person about 9 months behind the gun press hoopla.