Is it because when I summon it it only seems to let me through despite other people trying to get in the portal
If you mean going through the portal from The Oasis, to get to The Tomb of Storms, then No, that is not a "solo" entry point.
Sometimes players do not have access to that area yet, and when they see that you summoned it to open, they hope that they can just jump on, and ride along with you. They don't realize that they have to follow the storyline quests, and they will get access on their own.
