Getting from one Verse to the other universes has always been a difficult task. When Wobblers have tried to get beyond the Mu Verse, and series of sub-verses called the MU Continuum, things have gotten a lot harder. Some would say that this Mu-Lambda Barrier is downright futile and dangerous. Of course getting to what is now called the Alpha Verse, it should technically have been named the Nu Verse, to the Mu Verse has been hard as well. By all accounts, it has been more difficult to traverse with more fatalities among inter-dimensional explorers than any other studied explorations. Still the M-to-L azimuth is a frontier that has not been breached to date. Expert Wobblers and collections of trans-dimensional theoreticians are more than a little perplexed as well as challenged.
The Omegans, residents of the Omega Verse, the first trans-dimensional travelers recorded and the ones that are the developers of the accepted universe naming conventions, lean towards thinking the farther that one gets from their universe, the more difficult things become. Part of the basis for this theory is that are no Wobblers passing through their territories displaying greater technologies and means that they have. It boils down to their presumption that the Omega Verse is the pinnacle of existence and that its reality blends into the universes beneath it. The farther away one gets, the harder it gets to move into others.
A bit less slanted resource for study of this matter happens to the Pi Verse, where the Greatest Empire, despite all of its technological inadequacy compared to Omega Verse, has still lead a vigorous exploration of the trans-dimensional space around that universe. According to their findings which credits Wobblers from other universes, as well as their own, they've noted that it is based on the individual explorer. Explorers tend to have problems with wobbling beyond their immediate neighboring universes. Depending on their expertise, they can greatly aid other Wobblers getting anywhere, but trans-dimensional travel seems to be a locality-based function. Of course these later findings may be propaganda from those that benefit from the stated release, namely the totalitarian Greatest Empire.
Less prominent trans-universal traveling powers tend not to have many releases about their own metaphysical explorations, or at least they aren't very transparent if they are.Those that do tend to exaggerate. Various entities from the Omicron Verse claim to possess the ability to travel "everywhere in the multiverse." After extensive studies into their human (and other sentient beings) sacrifice-laden spells, both the Greatest Empire and the Omegans find these claims to highly misleading. These "infernal" entites from Omicron proclaim supernatural spells. They also tend to have "tunnels" to very specific parts throughout the known Verses, but are much more at a disadvantage when traveling across them without them. These disadvantages tend to negate any of the shortcuts for Wobbling for the spells' authors. In this case, why bother if it isn't worth the time to get there?
Less abstractly, Mu-Nu Space is a new phenomena to established Wobblers. Traveling between the Omicron Verse and the Alpha "Plane" is extremely difficulty, but getting from it to the MU Continuum is about average in adversities and danger. No one, as of yet, has been able to move beyond the Mu Verse into the next universe though.
Still the Mu-Lambda frontier plenty of opportunity and even reward for the explorer. While the MU Continuum gets expanded there are plenty of "next-Verse" locales being discovered all the time.