I was always tempted to multi class my barbarian but those sweet sweet abilities just kept popping up.I've found that with groups that actually play every level, rather than start at a higher level, multiclassing drops a lot.
I suspect it's because there is always something good coming up in the next level that you don't want to delay/be behind the other players. For example, getting an ASI is pretty impactful. And what fighter wants to stay at one attack per round when the others now get 2 at level 5? So they put off multiclassing.
But start at level X? Much easier to do a multiclassed build since you don't have to actually experience those delays