Rounding up a party/alliance through shouts/yells doesn't necessarily mean you can complete them. After getting the people together, there's always a chance they will leave, go afk, etc. Losing your tanks or healers can ruin the entire alliance.
Without a Linkshell to run with, you're never guaranteed anything.
I do agree with the OP, in a sense, that everyone should be able to experience this content because of the point I stated above.
The arguments mentioned in this thread about other content relying on clears to proceed further don't point out that it's almost all soloable and duoable now. Voidwatch is a different story.