Think of how easy a 9.3.1 client install is/was.
Think of how not easy a v11 client install is.
Thus the difference.
I'm in the middle of 22.214.171.124 and am reminded as to why I always claim, "I don't do installs". Actually, it's a lot better than the whole System 9 install, but for those who just want Essbase...not so simple.