For some reason people seem to think that Blaze being from a separate dimension isn't a storytelling hurdle at all, and I really don't know what franchise they're following, because it sure as hell isn't the version of Sonic I know. Yes, in theory it could be as simple as just using a warp ring to hop over to the Sol Dimension whenever. There are ways to write around it. I'd love to see that happen so that we could flesh out Blaze's world some more. Give Blaze some more allies and villains of her own! Give her more to do over there, and more reasons for Sonic and co. to visit! But clearly Sega isn't down with that, considering the Sol Dimension has only ever been in one game and, what, two issues of the IDW comics for maybe ten pages total? Sega's just sitting on it, and it's impossible not to see the fact that it's a whole separate dimension as the reason.
Even if we were getting more stories about traveling to and from the Sol Dimension, it'd still be a hassle. You want to use the Chaotix in a story in the Sol Dimension? Wanna use Marine or Johnny or whoever in a story set on the main world? Well, you'd better think up an airtight excuse for why those characters are traveling between the dimensions and pray that Sega approves of it. And right now that seems to be one hell of an obstacle, given how little we see of the Sol Dimension even though I know damn well Ian and Evan would love to explore it more. It's gotten to the point that Blaze is now on an endless "vacation" on Sonic's Earth so that they can actually use her in stories. People have been acting like merging the worlds would completely take away everything that makes Blaze special as a character, when it would just make all of her personal story stuff infinitely easier to work with than it is right now.
"Oh but what about the Sol Emeralds?" There's no reason the Sol Emeralds couldn't exist on the same planet as the Chaos Emeralds. We've already got other magic rocks like the Time Stones, the Phantom Ruby, and the Warp Topaz. "But what about Eggman Nega?" I could not give less of a shit about what happens to Eggman Nega and Sega doesn't even use him anymore, but also he's already supposed to be from Silver's future, not the Sol Dimension. "But what about the plot of Sonic Rush where the whole point was that they had to stop the worlds from being merged because they thought it was a bad thing?" Yes, because Sonic has always been a series that treated canon as sacred an immutable, and Sega would never do something that contradicted a game from almost 20 years ago