I don't think people repost old content! They are cross posting their Dtube links cause You can't directly post a Dtube video in a community! If you click on the links of these cross posts you wil see that the posts are fre$h. I guess you are using Steemit.com. The interface it's kind of broken that's why these posts look weird. Check out the community posts via Steempeak.com
https://steempeak.com/c/hive-173115/created

Feel free to post your older videos though, I (@knowhow92) was injured for a couple of weeks now and I was sharing older clips too! I was just messing a bit with the editing so the look different! We will upvote and resteem every skate post within the community ;)