They are "cultural artifacts" and likely he doesn't know how to de-activate them. He probably assumes they are open because of Dante and that stopping him will close them.
With level design I agree backtracking isn't fun, but it's nowhere near as bad as people claim in DMC4. The levels all change in a specific way and you have a new char to play with. Thinking about it with regards to DmCs mission length, there's prob about the same amount of "original content" in both games. It's just in DMC4 there's backtracking and DmC there are whole missions dedicated to boss battles + the trade mission.
DmC has the most originality in the series most of all though. Mainly talking about the aesthetics and overall design. The art direction is absolutely incredible and probably the most memorable visuals I've seen in a video game in recent memory. Only other games would be Journey for being absolutely stunning and The Walking Dead for really capturing the comic book style perfectly. (talking in a more recent sense)
The last thing Devil May Cry ever did was take any kind of creative liberties because everything in that game is lifted from something else. It's kind of like Halo. The setting is nothing special at it fits just as well with a Castlevania game and characters are definitely nothing to write home about. Dante is obviously Alucard and Cobra if they maybe did a fushion dance and the overall plots are nothing to get excited about. DMC 3 is a shameless rip off of Inuyasha.
I'm not saying DmC's story is any better but it also isn't any worse. The narrative is definitely stronger in DmC than any other game out of the bunch by sheer presentation alone with the best voice performances in the series to date. The heavy over the top social satire also pays homage to Devil May Cry's natural absurdity which makes DmC also strike me as the most self aware of the bunch. It knows exactly what it is. Devil May Cry kind of had a thing where it couldn't figure out what it wanted to do. Like half the devs wanted to stay silly and the others wanted to get serious and they met each other half way. It's why you have such a change on tone from a game like Devil May Cry 1 to 2 then 3.
Overall, the one thing Devil May Cry never could grasp was consistency making the reboot no different to this trend. Why people flipped so goddamn much is beyond me. Overall, it's still Devil May Cry at the end of the day. Just instead of the generic anime wallpaper we have the most contemporary setting. I'm not saying it's the best thing I've ever seen but it sure as hell isn't any worse so it isn't a big deal to me. I think the fanatical fans give Devil May Cry, of all video game series, way more credit than it deserves.
Look the original game is still my favorite out of them all and I think it's the best. DmC though does get more hate than it deserves. It surpasses the originals in aspects and it was a step in the right direction for this series pushing 12 years old that honestly did nothing fresh or interesting as the years went on. DMC 4 has a solid combat system but the overall package is pathetic, lazy, and awful.
It deserves no excuse as it was an obvious cash grab and nothing more to milk the Devil May Cry brand. Prime example of a series being pushed through the ringer. A lot of people were p!ssed dropping 60 bones on a game that was a waste of freaking time that sure as hell didn't live up to the expectation that was expected after DMC 3. It was utterly submitted to the narrow minded anime fans who think everything from Japan is the superior everything. And even those annoying little f*ckers deserved better.
Capcom obviously doesn't care about Dante or Devil May Cry. Hand it off to someone else then Capcom and f*ck off. NT at least went forth with creative confidence despite being bashed by one of the worst video gaming fandoms out there at every turn. I'm all for something called creative integrity. The final product was not as bad as the fanatical fans try to make it out to be. In no way shape or form. The first is still the best to me, but DmC is NOT a bad game nor a terrible Devil May Cry and I think I know what Devil May Cry is all about mores so than most. I've been with this series since the demo showed up with Code Veronica. DmC deserves to continue at least for now. I want to see a more polished DmC next instead of reverting back to the previous series so soon. If it does revert, then you know Capcom is just selling out and I don't know if I'd play it at all, good or bad.
Ambition shows you have soul.