Why now? The NRA is sponsoring a race for the first time. Right or wrong, the NRA is a polarizing organization these days. I suspect their sponsorship has drawn attention to the guns in the ceremony from those previously unaware of it.
What are some sponsors problems? Again, pure speculation. Sponsors may not want the gunless majority to be assumed the sponsors share the NRA's policies.
NASCAR blows in the wind of public opinion. It wasn't that long ago you could find Confederate flags painted on cars and track signs, or get free cigarettes and chewing tobacco on souvenir row. Now you can't smoke inside many tracks, and golfer Bubba Watson caught flack last year when he wanted to bring his 'General Lee' to the Phoenix pre-race festivities. NASCAR may decide there are more non-gun owning race fans than owners, and more profit in catering to their opinions. Ceremonies come and go; you don't see half-dressed trophy queens these days (and more's the pity). Burn-outs have replaced victory laps (even the Polish ones).
As to kissing the bricks, it wasn't an official part of the Indianapolis winner's circle ceremony. Dale Jarrett's team chose to do it on their own (the entire team), and other teams have continued of their own accord. That's what makes a tradition. The Texas track personnel bring the hat and guns to Victory Circle and orchestrate the photo shot. I suspect if they didn't, few drivers would ask for or miss them. To the drivers, it's probably just one more hat to swap, one more photo to pose for; it's the boot-shaped trophy they'll be taking home. Now that I do think is unique. Not a grandfather clock, but different enough that a casual glance tells you where it was won.