I love Gintama. I think it's a more memorable series than, I dunno, Assassination Classroom (which is only remembered when we talk about bestsellers). But, c'mon, if the series gets cover in its final chapter, I'll automatically think "yeah, this new editor-in-chief is really changing things" LOL. Not because the title doesn't deserve it. In fact, all the series over five years old or with good sales should get cover at the end, don't you think? But that's not how the magazine works. That's not how capitalism works. There are even rumors that Slam Dunk only received a cover by mistake, the cover would be to celebrate the end of the match, but Inoue said "f*ck it" at the last minute, and finished the manga as a whole, leaving fans and mangakas like "what?!" (find his interview with Fujimaki). So, if Naruto, one of the most iconic titles ever, inside and outside Japan, didn't have what it takes to achieve such honor (something that even left Oda surprised), it's natural to think that the adventures of Gintoki don't have it either.
It would be like giving a star on the Walk of Fame to Rihanna, but not to Beyoncé.
Sorry, the TV was showing a music video of them here and I thought the comparison would be appropriate. XD